I love PDN since years and gladly purchased the Windows Store version (yay for automatic updates), but had to go back to classic version because of an ancient UWP issue.
short version : I'm using a mouse and keyboard with programmable buttons, and none of these can be used with UWP.
long version : specific mouse and keyboards (mainly sold for gaming purposes) add shortcut keys and buttons that can be macro'd to shortcuts for specific programs. This is usually done through the mouse/keyboard drivers that monitor the active program/window and bind the keys to their relative shortcuts. For example purposes, here's some docs :
Logitech documentation : https://www.logitech.com/assets/51813/3/lgs-guide.pdf page 52, step 6
Razer documentation : http://drivers.razersupport.com/master-guides/Razer%20Nostromo%20MasterGuide.pdf page 4, step C-5
Alas, UWP programs don't have any exe files that can be linked to these profiles. The only workaround is to use a permanent profile when using an UWP app. This is an old problem (as shown in a February 2016 article : https://www.howtogeek.com/243012/why-you-shouldnt-buy-rise-of-the-tomb-raider-and-other-pc-games-from-the-windows-store/ : search for "no .exe file" ) that still has no solution and can not be solved by peripheral makers : https://www.reddit.com/r/LogitechG/comments/536snw/logitech_gaming_software_and_uwp_apps_windows_10/
So I'm reinstalling classic PaintDotNet and keeping my UWP license in the hope that Microsoft will work with the peripheral makers to negociate a solution. In the meantime, please do not depreciate the classic PDN :)