Starting with Signal 6.21.3 you can camouflage the app by using another icon (like “News” or “Weather”).
I immediately tried on an XA2 with Sailfish OS 4.5.0.18, and it eventually worked.
For a nervous moment I couldn’t open the app anymore, but after a restart (and some more moments), the new app icon appeared at the bottom of the app grid (just like after the update with its new handling of Android icons).
In a way, the Sailfish droplet shape is now a second layer of camouflage…
Just wanted to let users know in case they’re wondering what might happen.