Hi @toastwine, that sounds great!
The instructions are a bit outdated, especially after the move to .NET8 in the master branch.
To debug, you just need the .NET SDK installed, then you can do:
git checkout https://github.com/duplicati/duplicati
cd duplicati
dotnet build
dotnet run
If you prefer an IDE, there are support files for VS Code in the repo, so you can just open the checked out folder with VS Code and choose one of the debug options (TrayIcon is probably easiest).