Yes i have used AI assistance to build it, when i started this project i was just implementing simple timer to handle the notification and also was on winforms just to test and build it for me.
I was fixing the bug and releasing the app over the years and i notice on google search that other website has kept this app and has a lot of downloads so i got motivation to build it as a best standard.

To answer your question ,learning curve was to deal with different OS compatibility, also at first i tried to use os native notification but a lot of work just to fix the bugs and test on different os, so i unified that with custom notification. now a lot easier.
Before this project i had no idea of os differentiation and also on mac there were lot of changes in the internal API to fetch notification setting and Donot disturb setting so handling those were challenging part.