The header has several messaging options, also for USP messages.
Special message (top of the page)
This theme has the option to display a special message that comes up after loading the page, and will not appear until a certain expiration time, measured in hours. This message will only appear if you enter your own message content, so if you do not enter that content, this feature will not show.
The translation key for this special message content is "notification content".
USP messages can be added to be shown as a carousel (no auto-play) via Translations.