It’s the other way around. Players cannot build when out-of-bounds – full-stop.
To disable the map border that exist by default on maps, use Use_Legacy_Clip_Borders false in the map’s Config.json file.
You can then create your own map border by using Player Clip volumes. Note that the Player Clip volume has a toggleable setting for “Block Player”. When this is enabled, it blocks the player from passing through the volume. When its disabled, players can pass through it but are considered “out-of-bounds” and cannot build.