On dimensions created with a Datapack, you cannot view/set a world border.
MC-190482
World Border on datapack dimensions does not show up
Resolved
Duplicate
0
Thank you for your report!
We're tracking this issue in MC-121997, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki