If you have the ability to disable UPnP on the router, then you presumably have the ability to set up port forwards manually. "Don't want" doesn't come into play; if you disable UPnP, that's the trade off you're making.

I mean, I don't want to disable upnp. The whole point of it is to not have to do forward manually. So my question is : if I want automatic port forwarding, and given that apparently UPNP is bad for some reasons that I don't know, then what are the other automatic options