This is my (somewhat costly) solution to creating 1080p or 4K 60fps videos using DAIN-App:
If your video is native 1080p, downscale the video first to 848×480. I use a bicubic sharp filter to downscale the video in avisynth. This should retain as much detail as possible.
Next run the video in Dain-App. Converting should be much faster than using the Split method.
Here comes the somewhat costly part: Buy Gigapixel (The free beta is sadly over) for Video to reconstruct the video back to 1080p or make it 4K.
Basically you are using 2 AI programs to create your ideal video creation. Hope that helps.
I have a RTX 2060 + Ryzen 7 CPU and converting videos @720p is way too slow for anything over 5 minutes. AI upscaling is the only way IMO.