[aloer]

That one still seems to be 45x45mm. I am now using Philips hue smart buttons which are similar in size.

The tiktok ring on the other hand manages to put a simple button, bluetooth, battery and usb port all into a package of roughly 6x10x4mm

[n4te]

IKEA Symfonisk is 50mm round but it has press and rotate. I was actually thinking of Aqara WXKG11LM. It's 45mm square with round corners, but only 12mm thick.

Otherwise you can look at the Picoclick. It's 18x22m (height unknown) with no enclosure, with is 20.6x22.6mm and 11.6mm tall. Smaller than that is probably hard. I have never seen the Picoclick in stock, so you might have to build it yourself. It seems like a neat product, it's too bad the creator doesn't make it available.