From Liquipedia Overwatch Wiki
Push is a gamemode introduced in Overwatch 2.
The two teams fight for control of a robot who will travel in the teams direction and push a barricade. Whichever team pushes their robot farther when time expires or all the way to the end of the track wins.
A checkpoint at the midway point of each team's attacking path unlocks a forward spawn for the attacking team, which remains active until the bot crosses into the other team's path. It unlocks again after it passes the original checkpoint.