Edge supported epub until the bitter end of the Spartan renderer. It was only Microsoft's attempt at an ebook store that died long before that. Admittedly, most people's visibility into Edge epub support was through the Store and the sidebar dedicated to store purchases, but if you had no other book reader app take over the .epub file extension (or if you realized that you could drag and drop DRM-free .epub files into new tabs) Edge would still read them right up to the Chromium switch.
I think it was too. I also think a lot of people missed that there was an app in the Microsoft Store from some team adjacent to the Edge team at the time called the boring and easy to overlook name "Reader" that just had the PDF and EPUB viewers from Edge in a file-based UI instead of browser chrome UI. It was such a useful app and you could set it to default for PDF (in Windows 8 and the early years of 10) and EPUB files (in early Windows 10, with some effort). I never understood why their ebook store effort focused on a sidebar in Edge that didn't work like anything else in Edge instead of beefing up a file-based app like Reader. Reader also died when Edge went to Chromium and I still miss it as a lightweight and fast PDF reader.
