I tend to use a vanilla vim for everything related to tech stuff. Vanially vim allows me to keep being used to not having too much features, and I'll be fine even with busybox's vi, which... can help, on some systems.

For mails, I use claws's integrated editor, which... well, does not have any advanced feature, AFAIK.

And, recently (few days ago) I reinstalled zim (https://zim-wiki.org) on my system, because vim is not suited to write notes, and zim feels better on that point. There are still problems here, as I find it not easy to navigate between notes, but maybe I just forgot how that works.
I tried very quickly QOwnNotes, but I feel this will be a mess, and was shocked by the memory usage, Cherrytree seems interesting too, for that, but requires a too recent glibmm version (for my lovely debian), so I need to find a commit which does not requires that.