I would suspect that you're not using the kstars repository so the update hasn't been upstreamed to the Astroberry distribution (this normally takes a few days).
https://www.astroberry.io/repo/pool/main/k/kstars-bleeding/
Seems to still reference 3.5.4 as the latest as of 16/7/21
If you don't want to wait, you can add the kstars repository by running as below:
Dragons be here, please backup your sdcard, etc (personally I use borg backup before each change)
sudo apt-add-repository ppa:mutlaqja/ppa
sudo apt-get update
sudo apt-get install indi-full kstars-bleeding
I've just done this on both Stellarmate and Astroberry both fine.
However it actually looks like Stellarmate updated the repo on the 23/09/21
https://ppa.stellarmate.com/repos/apt/stable/pool/main/k/kstars-bleeding/