You can format your mash so the date and captions don't overlap with the TikTok watermark and orientation.
This is currently available on the iOS app only.
On the iOS app:
Open the mashing screen
Tap on the "Format for Tiktok" button to enable this
Notice that the date/caption text moves up a bit to leave some room for TikTok and Reels captions and that the mash changes its orientation to portrait if it was set to landscape
Tap on it again if you want to disable it and notice that the date stamp and caption go back to their original position