[squarefoot]

OP probably refers to Lenovo ThinkCentre mini PCs; they're well made, quite expandable and cheap, but if you can't find any, check out used Chromeboxes. They can be unlocked and reflashed with Coreboot in a single step, which makes them more secure aside allowing the native install of your OS of choice. Hardware quality is usually very good.

More info here: https://docs.mrchromebox.tech/

Chromeboxes aside, I've installed various Linux distros on different MiniPCs and the outcome has always been great; the only caveat is to check if your particular model does like to be used without a monitor. In some cases they didn't and refused to boot, but I solved by connecting on the HDMI port one of those cheap "virtual monitor", "dummy monitor", etc. dongles sold to perform this exact function.