The new Teams client does not use Windows notifications like the classic Teams client, and this is part of the problem. Not sure why MS removed that functionality. I, along with thousands of others based on the other threads out there, experience intermittent problems with calls coming through with no notification from Teams, and no way to answer the calls, other than to answer on the mobile device also signed in. FWIW, Teams is running on my secondary monitor. I do have everything enabled under Settings > Notifications and activity > Notifications. The new Teams client still seems like it's in beta/preview, even though it's not, and this is likely the reason Microsoft has pushed out the deadline to move off of the classic client (was May, now June) - in other words, MS finally realized how buggy it is, and needs more time to fix it. My advice, stay on Teams classic if you need notifications.