Stadiums in GTA have been mostly visible-but-not-very-interactive. Vice City Beach Stadium in the 2002 game had derbies. GTA V's Maze Bank Arena hosted side events. Trailer 2 has what looks like a stadium frame - we read carefully and don't over-claim.
For sports venues across the broader map, see the stadium locations page.
What the frame shows
A circular or oval roofed venue, large enough to read as a major sports facility. Visible parking infrastructure around it. Limited frame time - we don't have a clean exterior or interior shot.
Plausible analogue is Hard Rock Stadium or Loan Depot Park, both real Miami venues. The trailer frame is too brief to commit to a specific real-world reference.
What stadiums historically do in GTA
Concert venues. Sports event broadcasts (sometimes interactive, sometimes not). Side-content arenas - derbies in 2002, races and combat events in V. Story missions occasionally use them as location.
GTA Online has used stadiums for Diamond Casino events, Arena Wars and Stunt Race series. None of that is GTA 6 confirmation - it's pattern.