You can turn off auto updates of macOS and Mac App Store apps completely, yes. I stayed on Mojave for months after Catalina was released and I had a MAS app th

You can turn off auto updates of macOS and Mac App Store apps completely, yes. I stayed on Mojave for months after Catalina was released and I had a MAS app that broke compatibility with the same companies own (abandoned) self-hosted server software so I just didn’t update it. I’ve since resorted to running that single app (and the abandoned server app) in a High Sierra VM. The only version issues I know of that sound like what that other person referenced is: If you update eg iOS to a new major version, sometimes iCloud-linked apps will say they need to upgrade something for new functionality (Notes specifically did this at least once in the last couple of years and iCloud Drive did it a few years ago). But that is (a) not forced and (b) you’re told exactly what will happen (ie that older macs/iPhones won’t be able to use iCloud until they update too). Some third party apps will set minimum required OS version (ie to use a new framework or api) but that doesn’t sound like what the other post was talking about?