Spectra does it somehow, I am yet to figure out, how exactly. Spectra also gives out a 10.x.x.x (this changes too each time we connect) private IP address on the WAN side, but all I need to enable is uPNP and/or NAT-PMP. I can see the destination NAT rules which gets created by uPNP on my Mikrotik router and after that it just works."Buy it from the internet" - excitel customer care 2019
I have my doubts because even the WAN IP (in 10.xx range) changes every time we connect/disconnect it will be interesting to see how will they port forward to that.
Would be great even if they open some ports. Keep us posted.
So I went ahead and setup a port-forward for 443 as well and it appears to work with my current subnet. Many months ago where I had a web server running and was monitoring with Pingdom, what I observed is, at times it would just stop working even though my web server is up and running, but ports above 10k seemed to work always. Perhaps its just for some specific subnets, similar to the routing issues