I have watched a few youtube videos, and decided to play QFG 1-5 again as Dakota, the magical thief. I cannot load the game on Windows 10. Can anyone help??

You're not really giving any information on what exactly is going wrong for you. But if DosBox isn't working for you for the earlier games (1 to 4), you want want to try installing ScummVM. It also includes various bugfixes that running the GOG versions directly don't.

I'm actually experiencing a similar issue. I have been playing the games on Windows 10 without any issues for several weeks until I tried to fire up QfG 1....then 2.....and so on. 5 works fine. The other 4, it just shows "syncing cloud saves," the play button turns gray as if the game is about to start, then it goes back to being as if I had never tried to start the game. No error message or any indication of a problem, it simply doesn't start.

Definitely, the ScummVM versions are much better than the DOSbox ones.

ScummVM takes the approach of being a source port, whereas DOSBox is an emulation solution. This results in ScummVM generally performing better, but occasionally being inconsistent (sometimes in a good way, sometimes bad) with the original engine.

ScummVM also has 99 save slots!