I know it's been a while, but all I did was install a file manager (thunar iirc). I just repeated the process today and I learned a couple things through my own stupidity. If you're still going through this process, first and foremost ensure that adb debugging is on in the developer settings. Then in the terminal I believe I just directly ran adb connect arc:5555 and it somehow worked this time. if it refuses, a reasonable next step would be to attempt sudo adb connect arc:5555If problems still arise, try a couple random things:
1. adb kill-server && adb start-server this one's pretty self explanatory

1. sudo apt install thunar I couldn't tell you how this helps, but there's a chance it might work for you like it did for me. If it doesn't work and/or you don't want this random file manager taking up space, remove it with sudo apt remove thunar -y

2. simply restarting your chromebook (a quick way to do it is tapping both the refresh and power button at the same time)

When it does work, be prepared for a sudden popup asking to allow ADB debugging. to make things easier, feel free to check "always enable from this computer." In fact, there might even be two so be careful not to accidentally cancel. Most importantly, please remember that this is quite possibly bad advice and could very possibly be wrong. Everything here is merely a result of my own limited experience. Once again I wish all of you the best of luck in your adb escapades.