the new photoshops are so terrible.... how and why?

It's not Photoshop, it's advanced raster image editing. There's just an enormous amount of data that must be moved around. All that data has to go somewhere, so it's written to disk. This goes way beyond any RAM you may have installed.

The scratch file contains all history states for all open documents. Each history state potentially adds the full uncompressed file size. If you also use smart objects, the scratch file explodes rapidly.

The scratch disk is Photoshop's main memory, with RAM as a fast access cache.

For any serious work with reasonably big files from a modern camera, you will need 500 GB and up, preferably 1 TB. Especially if you have several files open.

I have 4 TB.

Indeed I have a mere 5GB of scratch space on my hard drive which only had 500GB to begin with.

Photoshop says it needs 50GB to open.  That isn't an app, it's an operating system.

Absolutely disastrous and unusable.

New versions also require 50GB of free harddrive space even for simple tasks on small images.  It is as all the worst programmers who were fired from Microsoft got scooped up by Adobe and decided that what we really needed wasnt a functioning app but instead a costly vending machine app.

i mean some of the new tools are good.... but not at the cost of crashing and display bugs and errors. When you have been using the sameworkflow for decades just a minor tweak throws you off so much. For deacdes photoshop was super solid and never crashed.... like never. Since 2018 i have had tons of issues daily.