Yep, C# and Windows Forms recommendation from me too. Excellent tooling, fine language, mature and straightforward tech, very popular over very many years so wide resources online.

WPF seems like a nice idea, but it's tricky to get into, has limited penetration/support, and it's never been very clear whether Microsoft have abandoned it or not (including to Microsoft, I sometimes suspect).

If it's a basic app, basic WinForms should do just fine.