No official announcement has yet made but accourding to The Store page the Game has joined the Vault in 28 Nov
https://www.microsoft.com/en-us/p/star-wars-battlefront-ii/c0gwtpd0s8s1?activetab=pivot:overviewtab
Soure
lock if old
https://www.microsoft.com/en-us/p/star-wars-battlefront-ii/c0gwtpd0s8s1?activetab=pivot:overviewtab
Soure
lock if old