How do I stop Adobe software from using so much memory?

Just as a note, I’m running Photoshop on Tahoe and what are now two lower-end machines- an Intel MacBook Pro w/16GB of RAM, and an M1 Mac mini w/16GB of RAM. I also always have Bridge open on the Intel and Lightroom Classic (with a 300k-image catalog) open on the Mini. The Intel consistently stays in the green for memory pressure, although the Wacom driver has a memory leak and has to be restarted ever couple of days. The Mini is on the edge of green/yellow for memory pressure since Lightroom is a pig. I very much want to upgrade both soon but both are certainly usable as-is.

Don’t worry about memory usage as long as the meter stays in the green. You WANT the computer to use available memory.

I had been dealing with the problem of Photoshop using up to 100% of my system ram when opening.  At times, it would not completely open.  I tried reducing the amount of ram allowed to Photoshop and that allowed me to at least get the program open but it still used 80%+ ram.  Photoshop also took longer and longer to open when it did open. It was taking 1 minute and 20 seconds to open.  Today I solved both problems in a surprisingly easy way.  I moved the Photoshop settings from Appdata to my desktop and let Photoshop recreate those preferences.  That’s all.  Photoshop immediately opened within 5 seconds.  Then I carefully moved some of my customizations back into Appdata one at a time to see if anything in particular was causing it to take so long to open but everything was fine.  Also, Photoshop’s performance when opening complex files is drastically improved.  Complex files open almost instantly.  I can’t even remember a time when Photoshop performed as well as it is right now and I’ve used Photoshop since the 90’s.  My guess though is that over time, Photoshop accumulates a lot of stuff in Appdata and probably it needs to be dumped and rebuilt from time to time.  I’ve never done that as a policy. One last thing.  My memory usage after opening Photoshop is down from 89% down to 33%.

This sounds much more like a GPU driver issue. Memory usage looks normal. Try to do a complete reset of preferences/settings. This goes beyond your own user settings, it's the entire application configuration including hidden and system-dependent parameters. Corrupt settings usually look like application bugs.

Photoshop doesn't slow down in low memory. It just writes to disk, physical memory is just used as a cache. The heavy lifting is the scratch disk. As long as you have enough free disk space, Photoshp will keep on working normally.

You should always have a couple of hundred GB free disk space. But if you're running low, reducing the number of history states will dramatically reduce the scratch size.