Margie, I often see that Upgrade notice at the top of the messages in my Inbox. It's easy to get rid of without opening that message.

Mouse-over the words Microsoft Outlook in the subject line. A trash icon will appear with the word Remove. Click-on that & the message will vanish. Until next time.

I too use an ad-blocker in Outlook which I believe is why it's very slow to fully load. I don't think it's Microsoft fooling around to frustrate me into upgrading.