We might need more info. Do you have trouble indicating lights on the dash, do you have the hands free symbol on the dash (indicating it is available).
Did you recently have an update installed? If you did, make sure your settings indicate location can be tracked (seems to default to no sharing when updates roll out)
I am experiencing the same thing. Got on highway 401 around Belleville yesterday and went to turn on highway assist. I got a message saying “highway assist not available on this road.” This was strange because I drive this stretch using highway assist all the time. A few days earlier I had tried to use highway assist and got the note about Privacy Settings which I didn’t understand and had to look up. You can’t change privacy settings unless you’re in park, so I pulled over and selected the necessary privacy settings to enable navigation and highway assist. Got back on the road and it worked fine. Now, it doesn’t seem to work despite the correct settings.