Once you see the alert, you can open it into a message, and bottom right corner of the message, you can set its pop-up preferences individually.
Ah, right! I remember that now (done it before to turn alerts off). Thanks. Hopefully someone
will still offer to share knowledge, and I can turn the alert into a message.
Are you the country Utrecht? If not, the offer might not even have been for you. Maybe the country Utrecht got the offer. But an offer which was declined by an AI is also strange. If it was for you, it should say "we declined" not not that Utrecht declined.
In general it is useful if you make a screenshot if something unusual happens and then post the screenshot here. That way we can better see what is going on. And in some cases the last autosave and/or the save game from the situation is helpful as well(but not in this case, because notifications don't persist in the save).
Yes, I'm Utrecht. It may have said "we declined", with Utrecht in the heading. As I discovered (above) the offer must have come as an alert, not a message, which I didn't see so it timed out. I've now had another such alert, which I changed to a message in future. I accepted that alert, so I'm OK now, I'm getting the knowledge I need.
Point taken about screenshots in future. Thanks.