Can't rearrange displays.

Are any of the displays showing the same content as the other displays?

Have you tried downloading EasyRes:

https://apps.apple.com/us/app/easyres/id688211836?mt=12

It will give you more finite control of each display than Apple's Settings/Preferences.

So it is upon restart the sequence reorders itself. That sounds like the detection that the devices are recognized by the graphics card on startup. One approach might be to put the cable from 1on 3, the cable from 2 on 1, and the cable from 3 on 4, and the cable from 4 on 2, and see if that still happens out of sequence.

"why I cannot adjust the arrangement of the monitors in system settings > displays?"

Are you using the usual method of dragging the rectangle that refers to the display and placing it relative to the other rectangle at a different spot doesn't work?

Is your System Settings/preferences locked so you can't make changes? If you see an orange padlock in the corner, that means you need to use the administrative password to make changes.

Is there a profile section with a school or business account linked? Any school or business managed computer needs to have the settings managed by them. They may not give you access to those settings.

If you always shut down your computer at night, its built-in optimization routines never have a chance to run. I would recommend leaving it up on screen saver, not energy saver overnight at least once a month.