On iOS, Pro users can export a mash in 4K resolution. The 4K option appears only when at least one snippet in the mash is stored at 4K.
Store new snippets in 4K
The Video Recording Quality setting decides the size of snippets you record or add from now on. Snippets you've already added keep their original size.
Tap on the Profile tab.
Tap the gear icon.
Select "Camera and Media".
Go to "Video Recording Quality".
Set the quality to either 4K at 30 fps or 4K at 60 fps.
If Storage Optimization is on for the project, turn it off first—it shrinks every snippet to 1280px, which rules out 4K.
Export the mash in 4K
Once at least one snippet in the mash is stored at 4K, tap the yellow export button in the mashing screen and select Best Quality (4K):
Important: If no snippet in the mash is stored at 4K, there's no 4K option, whatever the recording setting says. If every snippet is 720p or smaller, the app skips the quality picker and exports in Standard quality. Find out why the 4K or quality option can be missing.
On Android, mashes export in HD or SD; there's no 4K export.