The Locator Bar is a compass-like bar above the hotbar that was added in the "Chase the Skies" update (Bedrock 1.21.90). It shows the direction of other nearby players. Unlike Minecraft Java Edition, on Bedrock it is not controlled by the locatorBar game rule but by the playerWaypoints game rule – set it to off to turn the bar off server-wide for all players.
Requirement
You need OP rights to change game rules. See Grant OP Rights.
Disable the Locator Bar
You can run the command either directly in the in-game chat (as an operator) or via the server console in the dashboard:
/gamerule playerWaypoints off
Re-enable the Locator Bar
Set the game rule back to everyone:
/gamerule playerWaypoints everyone