Options to access NAT/PAT from outside

Looking for the options how to access PAT network from outside. I’ve got situation where ISP actually not giving public IP and you have no access to core router to map the ports. Just thinking that Synology has some kind of solution for that. Do you guys can think what can be done? Would be good to have possibility to share links to files from nextcloud.
My first idea was to do an VPN tunnel, but all the traffic must pass through the VPN server. Bit not efficient.
Thanks for any ideas.

It’s difficult, VPN is probably one of the best (own IP address) but the routed traffic is always an issue. You could use the TOR network, you don’t have to pay for traffic but it’s not good to share links or have large bandwidth.

If you have ipv6, you could try some ipv6-only service.