My go to for reliable Linux platforms is anything off-lease. Workstation class systems are extremely robust most of the time. I have some that have been in 24/7 operation since I bought them years ago and they’re showing zero signs of slowing down. I love it.

Ewaste is also a good place to look for still good but deemed unworthy of use by a faceless, soulless corporation stuff. Usually tends to be a bit older, but it’s usually fine.

Have fun friends, there’s no wrong answers.