Gnome’s default file explorer does allow drag and drop to add a directory (folder) to the left sidebar. It just has to go into the middle list on the left sidebar. You cannot add things to the top list by drag and drop. KDE is far far more customisable than Gnome, but changing too many settings can sometimes make KDE unstable. If you choose KDE, try changing only a few settings at a time. Gnome takes the approach of making it more beginner friendly by making it harder to break and providing an experience that Gnome devs think would be the best.

We all have a final deadline for finishing our backlog and experiencing as much as we can in this world.

Good job. You now have tons of data. Where do you show the ads?

That is correct. The best case is to write a script to make your desired changes, and then run it after each system update.
My own use-case is that I have a NFS mount-point for my Steam Deck to use extra storage on my NAS. After the first time I figured out how to get it mounted, I made a script to disable read-only filesystem, make all the changes to the system, and then re-enable read-only filesystem. After every system update, I just run that script once.