Hello, so I've acquired more info about this problem, and talked with some other people that had this same problem. I thought it was strange that people claimed they could only join a server if they set automatic port forwarding, because I don't think it should work like this, so I tested it, and I came to some conclusions that are somehow even more subjective than what I wrote in this topic so far.
https://i.imgur.com/btkM6Kt.png
This guy from the img kept trying to join this server, which works for everyone including me and is full most of the time, but he couldn't, no matter what he tried, until he changed his own port to a random number and was finally able to join.
I tested this out myself in some servers I'm normally unable to join, I turned on my own automatic port forwarding and set a random port and I was able to join. if I left and tried to join again, it wouldn't work unless I change the port to a new one again as if the previous one isn't working anymore. As strange as that may look, I swear that is exactly what was happening to me, and I can't think of an explanation for that at all. It happens to some other people.
What bothers me the most is: Port forwarding is now necessary to simply join a server (because I don't think it was needed before)? And what could explain needing to set a new port number every time?
So what I concluded:
● All people that normally can host won't have issues to join any working server because their port forwarding works fine.
●
Some people that can
not host won't be able to join
some working servers unless they turn their own auto port forwarding on and set a new port.
Off Topic
Off: I'm not sure if that's much related, and I haven't tried this in my new router (I believe my newest router can't host any game no matter what I try), but there was a case in which I couldn't host in the newer versions of SFD some time ago, and when I tried to play a Pre-Alpha version, I hosted and friends were able to join my game with no problem.