CPUs from around 2005 onward are all perfectly usable IMO for the purposes of x86 desktops. As long as it’s got x86_64, SSE4 and at least two available threads. I would even wager that Pentium 4 hyperthreaded models (Wolfdale?) are still acceptable if we’re really pushing it.

My parents are using a 3rd gen i7 and it works fine. My brother has a few computers, one is a 2nd gen intel, but I think he put Linux on that one. My home server was running on my 4th gen i7 until I upgraded it to my second gen Ryzen earlier this year after I upgraded my gaming.