ER-X: Port forwarding problems

Hello

I have some problems with port forwarding with my Edgerouter X (running OS v1.10.6).

I set up my home network according to Mike Potts tutorial / setup guide (which can be found here: https://github.com/mjp66/Ubiquiti/blob/master/Ubiquiti%20Home%20Network.pdf). So I also took his firewall rules etc.

I have followed many different documented approaches already with the port forwarding, e.g.

https://help.ubnt.com/hc/en-us/articles/217367937 or https://community.ubnt.com/t5/EdgeRouter/ER-X-1-9-1-1-can-t-forward-ports-Is-port-forwarding-broken-in-1/td-p/1961239 and various tutorial videos on Youtube but I simply cannot get it working.

This is how it all looks like in my setup:

Modem from my ISP is connected to eth0.

eth3 is connected to an unmanaged switch (TP-Link TL-SG105) where also the device (with the static IP X.X.3.241) is connected to which I want to connect to from outside.

I did not check "Enable auto firewall" but setup the following Destination NAT Rules, as the enabled auto firewall did not seem to work:

Does anybody of you great guys have any clue? I spent so many hours on it already and I do not see a way out (e.g. setting the Lan Interface to eth3).

Greetings and thank you so much,

Maatz