I am one of 12 owners of a Team. However, only I and one other owner receive notification emails when someone applies to join. The email allows you to approve or reject the request. We don't know why we are the only ones!
I'd like to make other owners recipients, because it's our best way of tracking who has joined the (very large) team and welcoming them. The Teams notifications aren't really good enough. I have checked all kinds of settings in Teams and can't find a solution.
Also, if anyone has any tips for managing membership of a large team I'd welcome any suggestions :)
As for why the other owners don't receive the emails makes me wonder if it has something to do with being a "subscriber" for the group or not. Not sure to be honest. Try using the Get-UnifiedGroupLinks to see if there are any differences when it comes to the subscriber settings for the owners in this particular team. If so you can use the Add-UnifiedGroupLinks.