[ygra]

All done with US International, but should be reproducible with other keyboard layouts; just that with, e.g. a German layout it might be harder to find digraphs that can be typed by forcing a non-combination for a dead key.

Firefox 81, Windows: Dead keys and the corresponding combination of letters where no single letter is defined by the keyboard layout don't even appear. I.e. I type ', and then s, which normally causes the digraph 's to appear, but here neither the ' nor the s afterwards register.

Chrome 85, Windows: The key sequence registers as just one letter, but apparently not as the ', which thus is marked as an error. This was also what I've seen in Edge (Chromium-based, probably similar version number).

Internet Explorer 11: Same as with Chrome. However, with the added bonus that typing a space seems to be impossible. No idea whether that browser is even on the compatibility list for that site, but it's all I have lying around here right now.

[Octouroboros]

Thanks for your very descriptive answer! At the moment, key combinations aren't nearly as well supported as they ought to be. I'll certainly fix this in a future update. Thanks again!