Does this run on x86/64 bit systems? Or this is for Linux smartphones more.

I'm using it on a Fairphone 5 since a while. Works flawless

Please dont link with a Google Amp link.

Just a quick thought. These days you can create a special partition in the first part of your drive and just boot from it. No grub, no config really. You might want to take a look at EFI and an EFI system partition perhaps?

One idea is perhaps to have more than one device? A tablet at home could be used in some scenarios, the rooted phone for some others. Maybe you have an old device laying around?

I do! Since a while I selfhost with my risc-v Unmatched board. There are prebuilt Ubuntu Server images available. Its mainly for software which you have the source code for, and are willing to build from source. I've made use of docker buildx for cross cmpilation a fair bit as well. Go and Rust has good support. A good start can be to check out the riscv-bringup repo from carlosedp. Its definitely early days though, you need to be pretty motivated. Debian support is scheduled for next year AFAIK.

So, what do I actually use it for? nginx + tailscale so far

Tailscale maybe? They have a mode where you can configure a site to site links, you could route the docker networks. https://tailscale.com/kb/1019/subnets

Just in case - there are also good linux desktop applications - check out Authenticator on flathub for example.

Jerboa. It ticks all the boxes, is updated, and looks good

Tbh, that's the only platform where it is needed?

My vote goes to Mullvad. Possibly Proton VPN as a second contender.

+1 for Organic Maps. Create an open streetmap account and contribute - its a game changer for me. Instead of a consumer, you're a contributor. (That goes for all OSM ofc)