Today the "Upgrade Network" function is always highlighted on my network admin screen. I have done some Googling and some people seem to think it's always supposed to be there... but when logging into a subsite as admin, I see that they are also receiving a notification saying "There are pending changes to your account. This message will disappear once these pending changes are completed." That is new, and it shouldn't be there.
It doesn't matter how many times I upgrade the network... the function is always there and the message never goes away. I have done some experimenting with Defender today and only noticed this happening after installing it, but I cannot say Defender has anything to do with it. I got the same issue on a test network, also after installing Defender, but have removed Defender from that test network and the issue persists.