It's my #1 most missed feature in Firefox, where you can move tabs individually between windows, but not in a group. Trying to split off a group of related tabs into its own window is so painful that I often just kill them all and manually navigate back to them in the new window. It's a shame that they wasted so much effort on the Tab Group feature just to abandon it, instead of adding a tiny bit of functionality to the existing tab interface.
What's even more frustrating is that multiple tab select works (at least, UI-wise it appears to), but then when you actually drag the tabs out only one comes along.