I think it open on the instance that it was posted and if it’s not your home instance, you can’t do much. A maybe more feasible way is saving the post, then going to your instance on your browser or another app that supports blocking and do it there.
deleted by creator
If you open a post and click on the icon between the save and the reply icon, it opens that particular post in the webbrowser. Might save some steps.
I think it open on the instance that it was posted and if it’s not your home instance, you can’t do much. A maybe more feasible way is saving the post, then going to your instance on your browser or another app that supports blocking and do it there.