The last review point could be mitigated by allowing to long-tap to select/deselect a single message

1. For many this is going to break muscle memory since delete worked like this from the very beginning. I'm not going to ask to add a toggle, since no one likes toggles, but inverting this behavior would be nicer.

I'm probably just being obtuse, but what does "inverting this behavior" mean? Oh, I got it, you mean regular clicks to (de)select ranges and shift-clicks to (de)select individual items. 👍

3. Ctrl+Click doesn't really work for Mac (it opens a context menu). And we already have several Shift+Clicks across the app, so I suggest to switch to Shift modifier.

This might be a little tricky, but I'll give it a shot. I originally set it up with Shift but that winds up actually selecting text in the page, which was super annoying, so I'll have to figure out why and then figure out if changing the cause of that breaks anything else in the process.

I originally set it up with Shift but that winds up actually selecting text in the page

Hmm, probably need to call preventDefault on the event or something along these lines