The best I've found is MoonReader+. Unfortunately, though, it is Android. Will run in Windows 11, but not perfectly. Can't simply double-click on an ebook, and open it. I am hoping that MoonReader+ will be brought over to native Windows. I've written them many times to this effect.
Next would be Calibre. Just the reader, basically. Although Calibre has other great features, such as conversion abilities.
You have to make adjustments, though, in Calibre reader options, to get it exactly as you desire. Strongly suggest inserting a paragraph of CSS codes in preferences. Review CSS various possibilities, like font, font color, etc.
Finally, Sumatra seems to be coming along nicely, improving appearance regularly. And it's fast.