Programming and reading.
You can start steam just fine without the packages. In fact, if you install without them, it’ll ask you to install them every time, but you can skip that and it’ll work, just 32bit games won’t launch
Edit: Looks like I’m partially wrong, as pointed out by a commenter below, steam currently only launches the 32-bit version of the client, despite support for a 5l64-bit client
555 is still in beta, so I wouldn’t be surprised if something doesn’t work. That said, I haven’t experienced what you have (on GTX 1070 TI), though using 555 causes lots of kernel errors for me. Checking dmeg might reveal something in your case as well.
I use it for everything, because I connected my external monitors through the eGPU. https://wiki.archlinux.org/title/PRIME has a few methods for running only selected applications via the eGPU, but I haven’t tried them. Edit: See also https://wiki.archlinux.org/title/External_GPU#Xorg for eGPU specific setups.
Can confirm, I’m using a dock (from Razor) daily without problems. Hot switching doesn’t work though, you need to restart X/your display manager to connect or disconnect the eGPU. I’d recommend the gswitch utility to configure the graphics card to be used (on X11). Haven’t tested much on Wayland, but I know that at least Gnome (Wayland only) has trouble mixing eGPU and the internal display if that is important.
The main reason for Ubuntu against Debian is the packages. For Ubuntu, they’re much newer, and with PPAs (launchpad.net), you can often get more and/or newer packages built by other users. For debian, good luck, you’re stuck with old packages (which is the intent of Debian stable, but not nice as a user, that’s for server)