The old Edge is one of the best Epub readers I have ever used.
The new Edge, I have no reason at all to use it over Firefox. I hope no banking website makes it necessary to use Edge, as it happened with previous Microsoft browsers.
Yep, it's a shame that they removed it and actively prevented me from using it even though I still have old Edge on my system.
Now I need to import epubs into Calibre to have a reasonable epub reader.
FBReader is available for windows, if you're looking for open source (keeping in mind that the Android version is no longer open source, so it's not the same FBReader). CoolReader is also available for windows.
Personally, I actually prefer calibre's ebook reader; if you dislike it, but do use a Calibre library, Calibre Web [0] has a (IMO) fairly decent browser-based ebook reader