Sarcasm? No. Everyone has a different environment; and software; and potential for things to go right, or wrong. Asking a question like “Why would it work for the first few years?” is basically unanswerable without investing a lot of time and guesswork. Like “Why is the sky blue?” – there is an answer, but the amount of effort or learning to answer it outweighs the need to.
I did tell you where to find the switch – it will be on your login screen; you’d need to actually look for it. There are not many places it could be (on the login screen) although it can vary between distributions – usually a toggle or dropdown showing X11 and/or Wayland. If both are present, you can switch. If not, you can’t. Simple.
X11 and Wayland are mutually exclusive, but can both be installed. Only one of the technologies are used at a time.
Wayland is the new kid on the block so to speak. As such, it’s constantly under development, and frequently messing up.
I use KDE/Plasma and that problem doesn’t occur with X11.
I just noticed @scotty65 mention that he doesn’t have that problem on Wayland. With that new information, we have effectively eliminated Wayland as the likely culprit.
Your problem is something else. What exactly? I don’t know. Probably nobody knows, unless they’ve had that very same issue, learned how to fix it, and bothered to leave enough information for others to learn from it. Let’s hope that’s the case.
Observation:- Many people tend to expect a solution to their issue; nay, demand it; and offer nothing in return. Sometimes there’s not a “thanks” for the assistance and research often done on their behalf. Oblivious, they might simply get what they want, and leave; with no ducks given .
Update:- I can confirm drag/drop of pictures is working in Google Chrome (and likely all chrome-based browsers) in both X11 and Wayland.
Extra:- You might want to google something like: “drag and drop not working in ArchLinux” seeing that Manjaro is based on Arch. You might get more streamlined results from that.