This is my view too. I'm not worried about the metadata that Google will capture in a single GET request. I think the talk about what other secret information could be transmitted in SSL is a bit overblown. The software making the request is open-source. It wouldn't be too hard to open up the requests if someone really wanted to.
For me, Joplin is about keeping my data private, rather than my existence. I'm sure Google already knows a lot about me just from ads. Adding the single data-point that I use an Electron app isn't much more. If the text of my notes was being uploaded for spell-checking, that would be diffierent.