Yes, combine is definitely a problem on Stadia and you cannot use a keyboard and mouse with the default Stadia setup which is the Chromecast Ultra they sell with the controller. You need go to a PC and use a keyboard and mouse for the sections which require combine. This feedback was submitted when early access was first released and I am surprised it is still not fixed as you can't get a main reward tied to a story line without using combine. This really needs to be fixed.

For portals are you talking about the purple waypoints? If so, on Stadia you go to the map, then press the Y button to show waypoints. Then you can select a waypoint and fast travel. It is not intuitive. You can't just move an icon over a waypoint on the map and click it like most games.

Another bug/missing feature is the lack of any combat log. If you watch PC videos you can see a dialog which pops us that tells you a ton of information about dice rolls. This does not exist on Stadia with a controller, so you really don't know why something happened. Playing on Stadia with a controller you are at a big disadvantage over PC right now. There is a lot of information on the Stadia/controller UI which is missing or very difficult to find. I really hope they fix this before a console launch.