Undo for plugins broken in C13

The first picture is fine because creating a new instrument track goes to “standard” project history, not the mixer history. However, the second picture does show a certain problem.

Yes, according to your observation, there seems to be an issue with Cubase 13.0.10 or your particular installation. Please, create a new bug report according to these instructions:

How to format a bug report - Cubase - Steinberg Forums

If this would be a big problem for you, you can use Cubase 12.0.70 for now.