I am using the latest BTT and the latest Vivaldi Browser. When resizing, the window size is calculated properly, but the whole window ends up being 5-10 pixels above where it should be. So, let's say I do a gesture to maximize a Vivaldi Window. It resizes properly, but for some reason is positioned such that the top is about 5-10 px behind the menu bar and the bottom of the window is likewise, 5-10px away from the bottom of the screen. This doesn't happen with Opera, Firefox, or any other Window. But Vivaldi it self also performs normally. Not sure who's but this is 
I have the same problem. I'm afraid it's a bug in Vivaldi not in BTT.
I tried Windows resizing with Keyboard Maestro. Same thing. The problem only occurs in Vivaldi.
More specifically, it appears that it only happens for me on the M1 Pro with the Notch when it is in default resolution on the laptop screen. If I change it to a higher scaled resolution, everything is back to normal. Got to be a Vivaldi bug.