As others have already said, Kate should work as text editor. I think, the only thing that's not built-in is base64 en-/decoding, but you can set that up like this:
That's for decoding. For encoding, just change the name to "base64 encode" (exact name doesn't matter) and remove the "--decode" from the Arguments-field.
This relies on a CLI utility called base64
, which is going to be pre-installed on most distros.
It's not entirely perfect, because it'll always insert a newline, as that's part of the base64
output. If you do want to get rid of that, you could write a tiny script and then call that script instead, but obviously, you don't have to.
You can also install Kate on Windows, if you want to give it a test-ride: https://kate-editor.org/
(The base64
CLI won't be available on Windows, though.)
Hmm, Kate has a feature called "Sessions", which might be able to do that.
You can create just one session and then in the settings, set it to always load that session:
Well, and there are those two checkboxes, which I've also marked. The "Newly-created unsaved files" sounds like what you want, but seems to be broken on my system. It just reopens an empty file for me. Is that also broken for you?