How do I open multiple scores in a single instance of MuseScore 4 please. There are a number of things that seem way easier in this new version though I have not explored very much yet, but there are some ways of doing things from MuseScore 3 that were more intuitive, or maybe I was just used to them but comparing scores side by side is something I use a lot.
You don't, easy as that.
See #338910: Tabs behaviour change - Opening two scores on the same window for some more details
And sorry, I've been to busy / lazy to dig that up yesterday...