Still using MuseScore 3. Even without the new sounds packs enabled, the latency typing notes on a (computer) keyboard is still too high. I would rather be stuck with the old version then deal with the unsettling 100-200ms lag for every input. It's quite an unfortunate trend that so many modern applications are neglecting basic UI responsiveness.
I've been heavily using MuseScore 4 lately and haven't noticed that type of latency on the Linux AppImage. My only gripe with 4 is the inability to open multiple scores in tabs. It opens them in separate windows instead. It makes closing scores in that situation difficult. If you have two open windows and quit one of them, both quit. If you instead just close one of the scores the window remains open with nothing in it. It seems to be a can't/won't fix problem as it has to do with their new soundpack system. It's probably the number one gripe users have with 4.
I think with 4.0 release, they were more focus on getting engraving more correct (among other big changes like the new sound system), and that resulted in a performance hit, but the 4.1 patch notes specifically say there are significant performance improvements, so it would be worth it to try it out again.
The audio driver still matters, though. If you're on Windows rather than a Mac, not using ASIO will always incur a truly incredible latency, even with real MIDI devices. Mac's Core Audio is quite a bit better in that respect, but pretty much everything ships with Asio4All for Windows users, and it's still an excellent idea to use it if you don't have an ASIO audio interface.
Actually, WASAPI can deliver quite low latencies (<10ms) and it can also operate in shared mode, so I would always prefer it over ASIO4all when using the built-in soundcard.
