That's great to hear, thanks for sharing!
I just bought a 9th gen that I was going to test out for a while to see if it would work for me or if I truly need to go to an Air or Pro instead- with the absolute heaviest load I would put on it being creating 5-10 minute videos in iMovie or perhaps Lumafusion (haven't used it before, but am thinking of buying it).
It would be fantastic if it works well on this device and I don't need anything more expensive!
Again I don't know about 4k, since the only times I have done 4k I have done it on A12X or M1, but 1080p editing is very smooth in Lumafusion with A12. A13 will be at least as good. Having said that, I much prefer a larger iPad for video editing so I use the 12.9 most of the time, and now that it is also on Android, my default video editing device has become my Samsung S8 ultra (14.6").
Davinci is unusable on A12 other than for very basic editing. You really need at least A12Z (or 1TB A12X) for Davinci, or even better M1. I only use Davinci for things that are either not present or not as good in Lumafusion, but Lumafusion is my main editor.