I have 3 monitors and want to have joined only two. However it's not possible 4 me (please, advice, if I am wrong). Each time I need to unplug the cable from the 3rd one to make it working OK. Only eyefinity quick setup and all in row (and switched off one too - cable unpluggung needed). As I remember, in old drivers it was possible, but now. Please restore flexible eyefinity setup, I see, that many questions, like this, are present already
You should be able to do that just from Windows now.
Right click on empty space on the monitor an go to display Settings an you can move the monitors there.
Many Users who use Eyefinity have been complaining that Advanced Settings have been removed from AMD Drivers in 2020.
This User found a way to make the Advanced Settings visible again in AMD 2020 drivers:
See if in Advanced Settings you can do the operation you want.
I want to run the 4th one separate from the 3 I'm gaming on and I have only been able to do this by unplugging the 4th BEFORE starting Eyefinity, don't understand why it can't be as simple as NVIDIA has it and really if I had none about this prior I would had just gone to the other side, haha. I now worry that that might cause problems always disconnecting the monitor for my setup.