Whichever one you wind up with, Dolphin as a file manager blows the monstrosity that windows has out of the water. For someone who's eeked out some power/efficiency out of windows usage it should be very pleasant finding out the standard software available for Linux these can almost always make you more efficient with less effort.

I use kubuntu. It's a good choice for people who don't have experience but are able and willing to search for answers.

KDE defaults are solid and utilizes a lot of Windows muscle memory, and being based on Ubuntu means that it's really easy to search for answers on virtually any question you might have. Plus widespread package support

I was going to recommend a kubuntu lts, maybe help install flatpak support