Rasbperry Pi is a popular choice as a SoC / SBC Linux board. But you have to use their custom linux kernel. Are there Linux boards with decent mainline Linux kernel support?
Are you married to SBCs? There are dirt cheap, pretty powerful and small thin clients floating around in ebay. HP G3 mini for example.
They seem to be the only product that occupies negligible space and is relatively affordable.
The other options are either more expensive or significantly larger.
Well, not really. The HP g3 mini is roughly the size of a paperback book and costs around 100€, depending on the specs. Similar devices of slightly older makes are even cheaper.
So, yes, they are physically larger, but still pretty small. Chances are, you don’t actually need a tiny device like a Pi, so you should at least consider SFF PCs.
Maybe check out the SystemReady™ stuff from ARM: https://www.arm.com/architecture/system-architectures/systemready-certification-program
You most likely do not want to run a mainline kernel / system. Run Armbian instead, it is Debian optimized for SBCs, it has a very good track record and sometimes is the only option after manufacturers stop creating images for their old boards.
Generic images / mainline kernel might underperform in your board, the GPIO and other low level components will, most likely, not work and you might burn your storage as logging and other I/O intensive operations aren’t tweaked for SD/eMMC. Armbian aims to fix all those issues and provides continuous system and kernel updates long after the manufacturer stops doing so.
I sold my Odroid C2 or something, as there was no support anymore… didnt know much of Linux, I guess armbian woul have been fine?