Valve pivoting away from MacOS is a consequence of choices Apple has made for their platform, many of which made it a more hostile place for Steam to exist. This is baked into the long standing Apple model of software distribution, where API and architectural changes inevitably obsolete software with Apple usually providing only a limited time window for cross compatibility.
You can still play your purchases on an operating system that isn't actively fighting against you running them.
You can still play your purchases on an operating system that isn't actively fighting against you running them.