Did you buy it new? (Store bought and still in sealed packaging) If so: it has to be activated and linked to the same account you used to fly your old Mavic (even though you're using a different flight app - DJI FLY instead of DJI GO4).
Even if...
Reading your post carefully, this does not sound like a problem with the gimbal, what you desribed seems to be related to lag and 'jitter' in the video playback (or the recording of the video in the first place).
What video codec are you using...
I think you'll find this is down to PDAF/CDAF failing to nail focus. Switch to MF: and have the peaking option set to high for better on-screen display as to when you hit best focus.
I had the same problem with night shots using my Mavic 2 Pro...
I was disappointed myself to discover that it won't work for navigating inside, but it will work to test DJI Custom Unlocks indoors, that otherwise require taking the drone outside to test, when a Home Point setting is required before they will work.