Should port forwarding for running bitcoin be done also on the ISP's router?
In discussion with @lenlord it seems that his ISP's router does not perform NAT so that his home router has (dynamically) assigned public IP address.

After reading some forum posts and contacting the ISP I found out that some ISPs (and mine is one of them) do indeed hide households behind their NAT (NAT 1 in picture, so called CG-NAT), but that they can remove this NAT for free on demand.

Remove this NAT on the ISP's router is needed to operate bitcoin node with incoming connections.