That’s a good idea

No.

But if you really want to use hashtags, you can check out Kbin. It’s kind of similar to Lemmy and has hashtags.

Or maybe let’s name the feature restricted community or something similar, instead of private community, to not make that fake sense of privacy

But in this case, if an app is open source, there is a higher chance of discovering that it sends your credentials somewhere else than in closed source app

Using open source apps, especially with more than one contributor, is currently the best option to be safe from this kind of attack.

Edit: I’m not saying that FOSS is 100% secure because it’s FOSS. I’m just saying it’s the best option we currently have.