I'm not sure what is meant by "specifications"
is that referring to current security updates, fully functioning web browsers, app compatibility, disk IO, GPU/CPU processing power?
not sure how to address without knowing the OP's focus, but
Macs function successfully with a very high HARDWARE percentage at five, ten, even fifteen years -- I see a shift in hardware percentages dropping in the immediate future with the maturing of Apples' soldered-in SSD, GPU, RAM because you can't repair them -- in the 2019 and earlier Macs you could replace the HDD/SSD, RAM -- now in 2026 you can't
WEAK LINKS in the M series silicon iMacs for their iMac screen issues, small integrated SSDs that get overworked and worn out (when the SSD, RAM, GPU fail, the machine cannot be repaired at any reasonable price) -- so what do you do with a machine that cannot be repaired (is the $2,000 question here)
the issues that destroy good working Apple 'vintage' Macs (2017 and earlier, for the purpose of making my point) are their macOSes have been dead-ended in big tech's "end of life" cycle to keep computer security healthy and cutting edge
Micro$oft is in the same boat with Windows 11 and 2019 hardware that doesn't support the newer security protocols -- Apple's 'vintage' machines no longer receive security, browser updates that can open them to hackers -- their web browsers no longer function properly (many no longer work at all)
my point here is -- stick to production model years, macOSes that will be supported for the time period you need them -- call it PLANNED OBSOLESCENCE or PROGRESS ...