Maybe try delta.chat? I use it, and it's quite good. Just make sure the guaranteed end to end encryption thing is on.
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Well, I guess we don't really know about everything on Windows either. Lots of people who use Windows haven't even heard of PowerShell or registry. It's not a requirement to know what they are and how to use them. They're just optional tools. You don't need to know absolutely everything to use Linux. There are many people who like (or need) to know about the more complex stuff, but when I tried Linux Mint, there was no need for any of that. It worked out of the box, and I enjoyed it. (Not saying Linux Mint is the best one! Distros are like colors, not everyone likes the same.)
Write. Anything you like. Nonsense, the issues of the world, a memory, a story. Sometimes, things (thoughts/memories) hurt less when written. Then you can burn the paper. Or tear it. Or do nothing with it. But burning it feels so good. It's like burning your sad thoughts.
If you might need to share anything to Windows devices (unlikely), Localsend is much better. Also I think Warpinator couldn't share text (maybe I just didn't see that option or it has been added), but Localsend can do that. But they're not that different.
I personally use KOReader for EBooks. You can download a dictionary on it and it'll tell you the meaning of any words you select. I suggest you give it a try. Oh, and if you wanted to read PDFs MJ PDF is great.