I can confirm that part of the Place marker add-on does not work in Edge. The command to set a mark, ctrl+Shift+NVDA+k does not work. When reading ePub books I use the add-on's specific find feature to find my place. It is a bit more cumbersome, but it works well. Of course the first prize would be if the app can be made to work in Edge as well as it works elsewhere.

Regards

Christo