Ah, so you're the kind who loves removed about things online, but won't lift a finger to defend themself, gotcha.
What I mentioned prior doesn't change anything about library management in the slightest, you just wanted an excuse.
Yes it is completely normal. The Internet is almost but not quite as bad as security wonks claim. Especially since you're not on the default port, most scanners don't have the programming to attempt on Home assistant. Most of them are built for more common exploits.
If you look at your proxy logs, you'll see attempts at various random paths, but those should all be 404 or 403s.
Is the one listed on Flathub not official?
https://flathub.org/apps/org.signal.Signal