I decided to move AppData to D: and created junction. I am not sure if it occurred because of this or because of Windows update shortly after, but ever since I am not able search for anything.

AppData is a major Windows folder and moving it has very most likely caused the issue (which will be exacerbated by Updates which assume AppData to be located with Windows).

A later comment was that the machine is desperately (your words) short of space.

AppData and like Windows folders (many of them) need to be located on Drive C: with Windows.

Solution here: Obtain a larger disk drive, back up your data, and then install Windows and all its folders on Drive C:

I decided to move AppData to D: and created junction. I am not sure if it occurred because of this or because of Windows update shortly after, but ever since I am not able search for anything.

AppData is a major Windows folder and moving it has very most likely caused the issue (which will be exacerbated by Updates which assume AppData to be located with Windows).

A later comment was that the machine is desperately (your words) short of space.

AppData and like Windows folders (many of them) need to be located on Drive C: with Windows.

Solution here:

(A) Move AppData back to C: if you can make space.

(B) Otherwise. obtain a larger disk drive, back up your data, and then install Windows and all its folders on Drive C: