See also the documentation of this app:
You can mark your snippets as private to exclude them from your mashed videos. This will allow you to comfortably share them on social media or with friends and family.
To do so, tap on the kebab menu (three dots) at the top right corner of the snippet thumbnail and select "Make Private."
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By default, private snippets are excluded from mashes. To include them, tap on "Include Private" on the mashing screen and confirm this action in the alert that will pop up.
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Private snippets are hidden from your mashed videos […] private snippet thumbnails are blurred on the calendar and day screen.
See also the documentation of this app: