I probably will not get any help here, as I am using Arch Linux (EndeavourOS) on my machine, I am also using the the 4.2 version of Simplify3D ( I am not a power user, I am satisfied as it is).
Though, I am hoping though that someone else have had this problem and solved it.
Note that I got Simpify3D to work in Manjaro (which is also Arch based), but I replaced Manjaro with EndeavourOS on my laptop.
So, I am getting 'Connection Error' when trying to login, with whatever password I am typing. So Simplify3d seems to not reach the the Simplify3D servers.
I have removed all the activations on my account on the website to see if that prevents me to login but it did not help.
I am running firewalld as firewall, and have tried disabling it ( I hope I did it correctly):
$ systemctl stop firewalld
It did not help.
Also I tried running my laptop on a different network (i.e. running on the wifi shared from my telephone), to rule out if it is my router blocking Simplify3D.
It did not help.
I have run ldd on the Simplify3D executable to search for any missing libraries, but everything there looks okay.
I think I have run out of ideas of making Simplify3D to run on my system.
The only thing I can think of now is if Simplify3D is using a special port number. If anyone knows the number, I can play with the firewall settings more (if I failed to disable the firewall correctly).
I hope someone else have solved it, or can come up with any more ideas to try solve the problem.