Could be a lot of things to be honest.
My colleague had to upgrade to "Monetary advantage for apple" last year as catalina was playing up big time on his very recent macbook.
He lost his collection of waves plugins, and I now can't open his logic pro (not X anymore) projects as they are not backward compatible with my older version so it makes collaborating a real mess.
Came here today because my 2012 macbook pro did overheat badly the last couple of days and then failed to start until it had cooled down at least twice in the past 2 days.
Got worried the fan had died but it's working fine when I checked with macs fan control so am thinking it might need some new thermal paste.