Depends on your threat model. But given more people using these things normalize it for those who can justify the need for such software (like whistleblowers, those organizing illegal direct action), it makes it easier for them to use it without it gaining too much suspicion and makes it easier for them to use it more consistently even outside talking about things that more obviously need that extra security.

Those are super easy to change, so no one would know that it’s you across different addresses unless you specifically tell them.

Or they recognize your writing (granted, unless you admit to it or do things like tell the same story on both accounts, it is basically just a hunch rather than solid evidence). I’ve accidentally done that with someone across websites once based on primarily based on how they wrote (granted it was a very niche community, making that cross-website different-username identification based on solely writing style much more feasible). If you write generically and avoid things like unusual emoticons (or intentionally write differently with different handles), its a lot harder to do that.

If they know what email and reddit it are, Lemmy should be pretty easy to understand, at least from a user-perspective. Replace reddit with Twitter/Bluesky for mastodon, Instagram for pixelfed, etc, etc. I don’t think understanding how email works at a tech level is important for being able to use it. Ditto for fediverse.

That your busy checking your emails