Make the window border more distinctive from the application behind it
The Teams window fades in colour to the bottom right which is where the corner resize handle is.
The colour at this corner of the app is often the same colour as apps in the background which makes it hard to find/grab the resize handle.
I wish I could comment with screenshots about how absolutely disorienting Metro/Fluent design language is. It's going to be a long decade until something new becomes the new hot thing in the valley....
The general design of Microsoft apps and the use of windows in Windows 10 make windows look more like graphical glitches with no depth or hierarchy to what windows are actually on your screen.