What about Foliate?
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Oh wow, this looks great! Thank you very much :D
Calibre is my goto. It can be somewhat complex but is feature-rich
This is the one!
I use KOReader both on Linux and Android, and I love it! I used Calibre's own reader for epub files earlier, but have since used a bit of time getting to know KOReader and its features better, and it suits my needs very well.
Sumatra PDF is easily my favorite, but you'd have to use Wine.
Don't know if you're into that kind of minimal, but lately I've been using epy and it is just amazing.
for simplicity I think sxiv supports ebooks