Spoof the Mac OS that is currently installed?

Doubt this is possible, but I love Mojave and don't want to upgrade to Big Sur or 64 bit. But Apps like Steam aren't going to support Majove anymore. Is there anyway to spoof other apps into thinking that my mac is actually running 11.0 or 12.0? Or do the apps actually run 64 bit and this isn't even possible? :(

Thanks!!!