@abj it was pretty bad before turning off 4k. Now it's at least playable.

The three wired buttons are strange...

https://i.ebayimg.com/images/g/YKcAAOSw5wli4NJJ/s-l1600.jpg

Others have evaluated these chinese knock-offs more closely:

The wiring harness is only compatible with the buttons and joysticks that china provides (but that does not stop anyone with a soldering iron!)

Full article here.

TL;DR: Reverse-engineer the button or get a new pushbutton.

@zenoxio You can bring up the RetroArch's RGUI and check how the Pad 2 is setup - is it set to 'RetroPad' or something else ? Might be that Genesis-Plus GX has a strange default for the 2nd controller, you could try lr-picodrive and see if the same issue happens.

Thank you, by any chance do you know a different bluetooth controller that's cheaper than this?
https://www.amazon.ca/gp/product/B07VFR96YS/ref=ox_sc_act_title_4?smid=ANP120TAQRWM2&psc=1

@mitu ok! i won't. hahah! i don't either, all i did, was also add it to the roms folder and it worked...hm?

OK, here are some final words:

I tried reinstalling Daphne and Ports emulators, which did nothing I wiped the SD card and started over.

After that, I attempted an experiment: with the RPi shiny and new, I changed the resolution with Raspi-Config and rebooted. The EmulationStation never came back. Apparently, in my case, changing the RetroPie resolution is a death sentence. For any reason, you'll never see your ES again.

Case closed.

@dankcushions, this is what I'm currently working on. I'll use the documentation Quicksilver mentioned to rebuild the old systems I want to transfer.

@ClassicGMR I have the same issue. I suspect it's user error!

Also, thanks :-)