Think about what happened in prior seasons:
Season 1: The "final battle" took place at t he school, at the Byers' house, and in the Upside Down - three places at once
Season 2: The final battle was in the tunnels under Hawkins, in Hoppers' cabin, and in the lab - three places at once.
Season 3 - the final battle took place in the mall, and in the Russian base under the mall - two places at once.
Season 4: The final battle took place in Vecna's lair in the Upside Down, inside Max' head, and in the Russia prison - three places at once.
Therefore, I predict the finale of Stranger Things season 5 will involve several things happening at different places at the same time.
