Hello,
This might as-well be a quite simple issue.
In the ‘play online’ menu there are several filters at the top. One of them (#2 in the screenshot) is called Source. It has to say Internet. If it doesn’t, click it until it says so.
If that doesn’t work, try the tool ailmanki posted.
Another option would be to use alternative server-lists like Trackbase. There you can see which mod the server is running and whether the players are bots or not.
To connect to the server you selected on Trackbase, simply:
copy the server ip (ctrl + c),
start the game,
open the console with ^,
hit Backspace a few times and write:
/connect “paste the server-ip here (ctrl + v)”
example: /connect 213.239.207.85:27960
Regards