I keep trying to open my photoshop and it keeps saying I have my scratch disk full (5,88GB). I erased my mac's cache and deleted some apps but it keeps saying I have the same 5,88GB and it's full....
How much space do you have on your disk? 5.8GB is not nearly enough free space, the operating system also needs free space to run and you will soon be hitting problems across all applications.
I've just opened Photoshop here in Windows 10 with 64GB of RAM (no documents open) and it immediately reserved 5.4GB on my scratch disk. Opening a multi layered file pushed that up to 15GB before I run any scratch disk intensive operations. That is no problem as I still have over 1TB of free space on that scratch disk.
It sounds like you need to free up a lot more space.