

The issue was much more straightforward than i thought. It seems sometimes thinking of too complex issues will hinder finding the easiest cause - the local forewall on the pi was blocking it / had no explcite allow.
To check i did: sudo ufw status verbose
There was only port 22
I added the new port as Allow Port 8081: sudo ufw allow 8081
And it works now! Thanks for all the tipps that pointed me in the right direction!
The issue was much more straightforward than i thought. It seems sometimes thinking of too complex issues will hinder finding the easiest cause - the local forewall on the pi was blocking it / had no explcite allow.
To check i did:
sudo ufw status verbose
There was only port 22
I added the new port as Allow Port 8081:
sudo ufw allow 8081
And it works now!