D2 game progress and licenses tied to Battle.net accounts had to be moved to Steam by players linking a Steam account to their profile and performing the PC Move function. This service was available to players from mid September 2019 through December 1, 2020. After 1700 UTC on December 1, 2020 that service is no longer provided and thus if you neglected to migrate your Battle.net information over to Steam there is unfortunately no way to do so now.