Hello @Marijus and thanks for taking the time!
I just checked my public IPv4 address via the https://www.whatismyip.com/ -service. It provides my ISPs-public IPv4 address block as the following:
ASN: 16086
Organization: DNA Oyj
ASN IP Range: 185.174.24.0/22
Note that I have specifically configured the APN from my ISP that provides a public IPv4 address. There is also an APN option that offers only a CGNAT-IPv4 address, which I am not using at the moment…
The DDDNS address works, and I can connect to the port forwarded -HTTPS-page via the internet, even when connecting via a third party VPN (Proton VPN in my case.)
I hope this information helps!