Same for me. KDE is so much better than Cinnamon. For Filemanagement, pcmanfm-qt (from LXQt) is the next best option. It is minimal, can be installed anywhere etc. Nemo lacks so many needed features.

For package management, a CLI upgrade from some old version of Mint to the current one worked kind of. But all the GUI stuff failed. I wrote a post about that.

And the desktop changed not a single bit. So many things that are missing, it is simply so traditional.