Libb

Neither Tuta or Proton will neatly integrate with Apple Mail if you want to send/receive encrypted messages. At least the last I checked it required for Proton a separate client that was not bug free (can’t remember for tuta).

If you don’t care about encryption, you may want to consider the Swiss Infomaniak.

They have a cloud offer which includes cloud storage (1to base), calendar and email, plus the online version of MSOffice, all being hosted on their Swiss servers.

I may have missed something, here so to make sure:

1. Do you want a wiki specifically, or are you looking for a tool that would allow you to easily create and manage some worldbuilding bible, be it a wiki or not a wiki?
2. Isn’t LibreOffice able to export to MediaWiki (Wikipedia)? I have not checked, and never used it, but I think it’s there somewhere.

the best thing it can do is just make a document look good,

It can also help you write the actual book, worrying about the document ‘look’ aka its formatting is optional (and if done properly, using Styles, it’s almost 100% automated) ;)

Wouldn’t a word processor do trick? you can add links, images, refs, notes,… and have as many pages as you need (edit: and search them, add a table of content, and so on). LIbreOffice is most certainly already installed on your Linux distro and is also available for Mac and Windows.