I updated the .NET Framework template for custom activities to run on .NET Core 6.0+ it includes several modernizations to the code to be up to standard with C#10. The project can be found on GitHub here:
https://github.com/Michael-S-Halpin/UIPath.HelloActivity
It includes a UnitTest project which will allow developers to step through their and debug their code outside of UiPath. It also has debug logging implemented to allow developers to optionally specify a log file which is useful for debugging from inside UiPath.