Sydney Sweeney got high at Stagecoach ... and, we mean that literally -- because Scooter Braun lifted her into the air on his shoulders.

Video is circulating online of the TV and movie star hopping on her man's broad shoulders for a lift during the festival.

Check it out ... these two are clearly couple goals -- with Braun standing firm while Sweeney sang her heart out to an Ella Langley song.

They've clearly got security ... but, no one is trying to bother the pair as they bounce along to the song.

Sweeney also rubbed elbows with a couple other stars ... singing with fellow actors Ashton Kutcher and Mila Kunis later in the evening.

These four weren't the only bold-faced names in attendance ... check out our gallery to see what other celebs headed to the desert for the festival.

Seems Scooter and Sydney are going strong as ... well, Scooter himself!