Hi @janine ,
Thank you for your reply.My Unity version is 2021.3.19f1c1 and I have tried it with the version Unity 2021.3.14f1c1 and Unity 2021.3.10f1c2,but I still have the problem and I have the tooltips.
But I found an interesting thing，My PC monitor resolution is 3840*2160，As you can see if I set my scale of screen with 150% the “+” button not useful when the window is small.But if I change the scale of screen with 200% the issue will never occur.So I think it may be an Unity bug.
Hope it’s help.