> it miserably failed because the OS required x86_64_v2 (I didn't even know this existed: I thought all x86_84 linux OS would boot on that machine...).
As the sibling comment mentioned, this decision was made for RHEL 9, so distributions based on the older RHEL 8 would still work for you. But that's not the first time it has happened: saying "all x86_84 linux" hides the fact that, for many distributions, x86_64 is all that's available on the x86 world; RHEL 6 was the last RHEL which could run on a 32-bit-only x86 PC. And even earlier than that, we had distributions that started requiring a Pentium or Pentium Pro or equivalent.
This ratcheting of CPU requirements happens for every Linux distribution; some are earlier (as you noticed, the RHEL world is on the leading edge of that), and some are later (Debian still has support for as far back as the Pentium Pro), but you cannot expect to keep using an old CPU on mainstream Linux distributions forever (or even on recent Linux at all; the latest Linux kernel no longer works on a 386 or 486 CPU).