I had the exact same issue with the symptoms you described on a 2023 Radcity Step thru.  This issue happened a few weeks after purchase with under 20 miles on the ebike.  A new controller got the Radcity back to normal.  Fast forward to Aug 2024; I have an error 21 on the LCD and all the same symptoms as before.  Rad sent me an seat post mounted external controller to replace the internal controller located in between the pedals. 

Check out Rad's video for the tools and procedure for replacing the internal Radcity controller.  Probably going to be the same steps and tools for the external controller.  The issue I had was the replacement internal controller wires were too long and I couldn't get the replacement controller seated properly inside the hole to insert the mounting screws from the bottom of the bike frame (it was wedged in there and I plugged up the screw holes to water proof). 

I won't have the long cable issue and probably faster replacement with the external controller.

https://support.radpowerbikes.com/Maintenance_and_troubleshooting/Controllers/RadCity_5_Plus_Controller_Replacement_Guide

Yup!  My spouse 2023 Radcity step thru had a controller failure a week after purchase in July 2023 (zero codes on LCD, no PAS/throttle power to rear hub).  The replacement controller was similar as the original; but, some of the cables were 2X longer.  Fast forward to Aug/2024 and I had an error 21.  The replacement controller was the external type that mounts to the back of the seat post down tube.  I haven't installed it yet.  We still have her 2018 Radcity Step Thru as a back up. We were going to sell the 18 Radcity and kept it instead because of the issues with the 23 Radcity.

No it doesn't...

Rad sent me a different controller that mounts on the outside of seat post down tube instead of internally in the space in-between the pedals.  Just haven't been motivated enough yet to start the repair. The wife still has her old 1st gen 2018 Radcity step thru to ride. The 2023 Radcity step thru was her new and improved upgraded model and we were going to sell the older Radcity.  I'm thinking I made the right choice going for a Himiway Cobra Pro instead replacing my 2016 Radrover with the latest Rover model.

I'm on my 3rd controller for the wife's 2023 Radcity step thru with under 300 miles. We live +5000 feet in the southwest; but, ride on level ground at around 14-18 mph max speed.  Long time Rad owner with two 2016 Radrover and replaced the controllers 4 times in first 2 years of owning the ebikes.  Zero issues with both Radrover controllers after 2018 (+4000 miles on each Radrovers).

I would like the option for physical key, keypad, or a wireless fob under X feet away for an ebikes to start it up for an added layer of security.  I've carried either physical keys, fobs, smartphone, or a wallet for +50 years and it hasn't been an issue misplacing for home, work, vehicles, travel, etc...  This won't stop the determined thief; but, limit the random "opportunistic" thief that keep electric/mechanical wire cutters in a backpack.

I have two 2016 Radrovers, 2018 Radcity, and 2023 Radcity.  I had brake pad rubbing and it would come/go depending on the braking situation.  I sometimes pump the brakes and that can more center the pads and reduce the rubbing sound. I've noticed all four ebikes had various tension for the spokes from the factory.  Around half of the spokes required 1/2 to two 360 degree turns to have the same tension (just going by feel for equal tq all around).  I think I had more rubbing because spoke flex because of my weight on the ebike being +270lbs compared to my spouse at 130lbs.

I also noticed one of my disk brake rotor wasn't true.  I used an adjustable wrench to bend the front rotor more true and that lessen the disk wobble.

It seemed like I always had to adjust my brake pads every month to the right brake feel, reduce rubbing noise, and emergency stopping power.  I eventually upgraded the cable to Jagwire MTB and mechanical calipers to TRP Spyke:
- TRP Spyke are direct plug-n-play replacement for my 2016 Rad's brakes
- pulled out Rad brake cable from plastic sleeve,
- used the same sleeve to insert Jagwire cable (purchased the cable only),
- cut to length at the caliper,
- added wire cap, and
- adjusted brake pads (TRP Spyke have L/R pad adjustments).

The spouse's Radcity was fine with original braking system and she only put +/- 300 miles a year compared to my +2200 miles per year. I only need to adjust brake handle tension when the brake pads wore down, I have fine tuning with L/R adjustments, greatly reduced cable stretch with no broken cable strands, less rust/oxidation on cable, way less noise when braking, improved emergency stopping power, and I don't get glazed pads like I did with original brakes/pads.

I went with the Velcro thumb throttle attachment for $19 from 1859 Northwest.  It comes in different colors, transferable to other twist throttles, and easy to adjust.

https://1859-northwest.myshopify.com/products/e-bike-thumb-throttle-attachment

I purchased a brand new Radcity Step Thru for my spouse July 23.  We put 17 miles on her ebike before having the exact same issue. Everything worked with no error codes; but, zero PAS/throttle to rear hub.  A bunch of back-forth trouble-shooting with Rad with videos. A new controller fixed it 100% and no other issues since.

It is usually eye contact, head nod gesture, and the optional lifting the four fingers off handlebars on the oncoming rider's side to wave in my neck of the woods.  This is usually from the more experienced riders with riding gear (not jeans shorts and not wearing a helmet type).

No details on mods for suspension, brakes, tires, bearing, etc... Not sure why this wouldn't be a (electric) motorcycle?  I wouldn't want to have a Radrover that can go +50 mph and having to do an emergency stop or have a mechanical failure at those speeds.  The fastest I've gone on my 16 Radrover was around 28 mph downhill and probably would have overheated the brakes if I had to do an emergency stop.

The wife (4'11", 125lbs) has a 2023 Radcity Step-thru and I have around 40-45 psi in the front/rear tires.  She also has the Cloud-9 cruiser seat and Cirrus Kinekt suspension seat-post.  I've notice her PSI drops faster per month compared to my fat tire ebike.  She can notice the difference on paved surfaces if the PSI is below 35.  She likes the way the Radcity feels at higher PSI; especially, at higher speed of 16-20 mph.

Is it a brand new or used battery pack?

I had something similar with my 2016 Radrover 11.4Ah battery.  I accidentally plugged in the wrong charger and burnt the internal fuse.  The battery pack worked as normal powering the rover; but, I couldn't charge the pack (same green light).  I had to take the battery pack apart and replace the internal fuse to get it work as normal (I think it was a mini 5amp).

I don't know if the newer battery pack have an internal fuse like the old ones?

I have two his/her 2016 Radrovers and the handlebars were too low for me (6'3"). A stem riser or taller handlebars wouldn't work for all family members.  The handlebars would be too high for my spouse that stands at 5" if we needed to switch ebikes or if my son needed to ride my ebike. 

I added the Sunlite 0-60 degree adjustable handlebar stem for the 100% solution.  I added the adjustable stem to both Radrovers and can then adjust in seconds depending on the rider.

https://amzn.to/3V02MYS

I have a 2016 Radrover and I kept my original tires in the 17-22 PSI range (always put 1-2 extra psi in rear tires).  Lower PSI provide better traction for dirt/sandy/rocky trail riding at lower speeds.  The higher PSI was more efficient, less power to maintain 17-20 mph speeds, and used less battery power when I did mostly paved road riding.

I just added the Fanttik X8 Ace Bike Pump 150PSI Fast Portable Tire Inflator, $50, Amazon, to toss in my topeak rack bag for easy psi adjustment on the road or trail.