The linked posts discuss this a bit, but to clarify for A6 Polaris specifically:
Use_Legacy_Clip_Borders false
toggles the default world border. This is, basically, a cube around the edges of the map, preventing you from going too close to the real edge of the map.
A6 Polaris, and some other curated maps (or Workshop maps) will disable the default world borders by default. This is because they might want to put something in what's normally considered "out-of-bounds". E.g., an NPC safezone, an Easter egg, some questline... Or, their map is a custom/weird shape, and they just need to manually create the map border instead.
Custom map borders (like the ones on A6 Polaris) are done with Player Clip volumes. In the Editor, you can configure volumes from the "Volumes" tab. Navigate to this tab, select the "Player Clip" volume, toggle its visibility to Solid, and then manually go through and delete all player clip volumes on t...
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