Dataminer explained why the ballistics shield was never added
Dataminer PlayerIGN explained why PUBG: Battlegrounds did not feature the ballistics shield, which the developers announced back in 2018, and which was originally planned to be added to the game in the same year.
I don’t know if I ever mentioned this before— the Ballistic Shield got cancelled because PUBG couldn’t fix certain issues with it att. Supposedly, you couldn’t turn or crouch while using it in-game.
In 2019, a PUBG: Battlegrounds community manager stated that "the ballistic shield is still in development." Since then, the community hasn't heard anything about the innovation.