Is it possible to configure for example 4 desktops and switch them separately for each monitor?
I think the following is appropriate to your question, unless you're asking about entirely separate displays and input (like a multi-user/seat setup):
I did this about 10 years ago as well. One "advantage" to the separate desktop setup is.... they're separate. Each monitor is a different $DISPLAY in X. You can run different window managers and DEs in each. The major disadvantage, as I recall, is that.... they're separate. there's no general way to switch a windows from one desktop to another. You'd have to quit the app and restart it on the appropriate display.
Another problem, is this require much mucking about in your /etc/X11/xorg.conf and I will freely admit that I haven't had to manually modify that file in many years.
I do not at all remember what I did way back then.
If you had a NVIDIA gpu, which you appear not to have, the nvidia-settings tool will explictely allow you to set the monitors each as a "Separate X Screen". This would eliminate manual modification the xorg.conf and that's generally a good thing.
On the AMD side? Here's a general discussion (old, I know, and not about an amd card, but it still ) that may give you point to start, perhaps: Non-Twinview Non-Xinerama Xorg.com. The key setting is
Here's my ServerLayout section from xorg.conf in the separate mode:
That pretty much did it. KDE worked, though Panels were only on one monitor. Cinnamon worked, but only in fall-back mode. To get anything on the other monitors, I explicitly had to change the DISPLAY to :0.0 or :0.1 and start another application. It would then appear on the monitor/display indicated. Once I seem to recall having had separate windowmanagers working, but my xorg.conf-fu is lacking these days.
Fedora has recently gained the multiseat capability (supported by a cheap USB box to which you connect monitors, mice, keyboards for different users).