WinForms is fine but there are issues with support for things like high DPI. Maybe that’s fixed now. I wouldn’t use it except for a very small utility, but nowadays I just use python scripts for small utilities.

Based on the .NET Rocks podcast, it sounds like Blazor is the new WinForms.

Given the situation with Windows, I don’t see it being a great choice for a monoplatform app (unless that app is a game) - chrome books and Mac are getting more popular, and web works everywhere.