Was playing Theme hospital yesterday, got to level 5 and the game froze and everyone is walking slow. Started a new game and the same thing happened. Uninstalled gog to install again and now it won't even let me reinstall it. I'm on macOS Big Sur Version 11.3. Does anyone have any advise? All I want to do is play the game!

You hit P(Pause) or 0-5 thats why they slowed down or stop.

Why you cant install, heh? Are you sure GOG installer is compatible with x64 (more correct mobile ARM-64 x64-only architecture, not even x86-64) Mac OS XI?
Current Mac OS and Mac PC cant handle any applications released before 2020 year (after complete migration from x86-64 - x64 - ARM-64). So even emulation mostly not work. You need virtual machine, or Parallels.