Maybe try switching the phone off, starting it without the SIM, then switch it off again, insert the SIM and boot it. Does your phone prompt you to install it now?
Otherwise, you may want to try another SIM card.
On which provider are you?
I’m on dual SIM: Scarlet (BE) as primary and Free (FR) as secondary sim. Will report back after I try your proposal. Btw, why would the simcard provider have an impact? Does it mean I should connect over 4G (not wifi) to get the update?
No, you should connect over wifi.
There were just a lot of reports in the past on the forum that the provider of the used SIM made a difference.
Probably the provider information is sent upon the update request and for some reasons (e.g. provider certification checks) the update offered depends sometimes from that provider.
So in your case this does not seem to be the cause of the problem.
For excample, there were numerous updates in the past that were not delivered to Vodafone customers. So if you can borrow a SIM from a friend who uses a different provider that would clearly be worth a try, at least to make sure that your SIM / provider is not the culprit here.
Should everything elses fail, then you could try a manual update as described in
Hello everyone. The problem was resolved yesterday. I did nothing particular except spent 1h30 in flight mode, but it could be a coincidence. When i deactivated the flight mode, the update notification appeared.