Rounded edges. 
I am disappointed every time another app switches to giant rounded edges and tons of padding/margins. It’s the trend, but I cannot understand why it’s the trend, other than being the Tailwind, Android, and iOS default style. It looks cool for about 5 minutes, and then the lack of utility follows.
It’s weird to defend round edges by stating they soften and humanize the UI. I actually want the opposite! My screen isn’t squishy, and my browser extensions aren’t writing poetry about love. Yes, a round button is a bigger target for a round fingertip, but you weren’t planning on using the negative space anyway (unless BW wants to try out a very, very experimental and potentially-cool-but-only-because-no-one-does-it-yet “bee’s nest” hexagon tile GUI; then I’m all ears, for at least 5 minutes until the lack of utility rears its ugly, giant-round-cornered head) and I’m very rarely on a touchscreen while using the extension. Round fingertip? What about my sharp-edged fingernail? The pointy tip of my mouse cursor?
It’s visually unappealing when done incorrectly (which a few people here have identified; BW is a bit guilty here) and it doesn’t serve a purpose when done right. I would much rather prefer sharp corners, careful alignment, enough padding to obey Fitts’s law and absolutely no more, subdued colors with good contrast.
(Sharp corners are in the Material You spec, but evidently no frontend designer ever reads that far, it seems.)
Menus should be loosely customizable and more difficult to get to based on how infrequently they are needed. I absolutely do not and will not use the GIANT SEND BUTTON on the primary dialog. It is a waste of space to me (but I’m sure other people think it’s swell). I don’t want to scroll at all if I search for a term but it has more than 3 matches. To add to that, I don’t need a big subheading element telling me THESE ARE CARDS, and this other group, THOSE ARE IDENTITIES; waste of space, little functionality or information.
That there is 12 mm between the edge of the extension dialog and the site icon? Waste of space (which would make the button width issue from @Nail1684 not so extreme) Between items? Well, I have 10 URL matches starting with address. but can’t even see them on a single screen unless I make the UI huge, which I don’t want to do either.
I would much rather BW focus on improving password field detection/filling than changing something that worked—presumably because Google wants everyone on Kotlin and Material You, but maybe because all the frontend new hires only think in terms of “xl:px-6 xl:py-1 xl:rounded-full xl:focus:rounded-3xl xl:border-2”.
You can’t autofill a password on the NXP registration website. The user field but never the password field is detected on any of the club login pages at https://vereinonline.org/
I’m sure there are many opportunities for improvements in this area, but instead we have the very visible (and mildly irritating) changes to the user interface.