I have 118 games in my library, 17 of which are Windows-only. Only 25 of the remaining 101 MacOS-compatible games survived the 64-bit upgrade.
Edit: thinking about it a little more though, this has been the situation for many many months, but I only realized over the weekend how bad it was because I've moved almost all of my gaming to my Nintendo Switch. (I only happened to return to Steam because I wanted to play A Short Hike.)
Plenty of FUD in that UI.
Also, Snow Leopard may have been the last version to support 32 bit processors, but I don't think support for 32 bit apps was deprecated that long ago? Certainly, Apple themselves was still releasing 32bit software back then—if you have a copy of iWork '09 (which got updated as late as 2012), it's 32 bit.
And while you're right it was deprecated immediately, I do recall universal binaries were soft and then hard deprecated some years ago but I could tell you the exact date. I know there's a lot of vintage software that would never be updated, but like, a good chunk of stuff seems to have been new development or continued support.
For non-games, a lot of the Mac software that was still 32 bit was using Carbon, which doesn't have a 64 bit variant. Carbon is old as heck, but if you're using it, there's no upgrade path other than a complete rewrite. That may or may not be worthwhile versus EOL'ing the software.
(As a complete tangent, I recently learned that Apple did once promise a 64 bit version of Carbon. The library was present in the developer preview of Leopard, and many devs began building with it. But then it was gone in Leopard's final release, and Apple never mentioned it again.)
You will never see Sony release a PS4 update that drops support for 2013-era PS4 games, at least not purposefully. If they did, people would be very mad.
I did saw Sony drop the almost unused GL ES support on the PS 2.
For example, one thing I noticed on the iOS side (when it went from 32-bit to 64-bit) is that pixel position rounding changed so you would see things like random one-pixel gaps where textures were previously adjacent, etc. These things add up, and a company might decide an older title is not worth fixing.
On the Mac side, the entire damned UI library was thrown out (Carbon), and it wouldn’t surprise me at all if games had been relying on it. That is a huge thing to just redo, and again I would not blame any game company for not bothering to spend the resources.
Lightroom 6 is the last standalone version that doesn't require subscriptions. It won't run on Catalina and has no good substitute on MacOS (I know about http://darktable.org/ but it is not performant or Mac-like on MacOS).
I doubt that Epic would have bothered targeting Metal in UE4 if it were macOS only. With it, building games for Macintosh for a great deal of developers is fairly trivial. Unity also targets Metal, as far as I am aware.
It sucks because I feel like gaming on the Mac was actually quite nice for a bit. With Steam/Source running on Mac you actually had a good run where you could play a lot of great games. I remember being so excited to play TF2 on the Mac.
The only games worth developing on the Mac are the 99¢ style iOS games. Anything else just isn't worth it, as developers have been burned too many times now. Just a matter of time before Apple makes it mandatory to use some technology or drops support for something that's currently required and everything has to be updated.
It's back to running games in a VM for me. Not the worst thing, really.
Some games do move forward to 64-bit but it will certainly require several years for the Mac game market (such as it is) to recover even to the point it had reached.