When you teleport to the world border and then use /locate Mansion, for example, it can show coords outside of the world. The image shows the proof. Tested in 1.15.1 and 1.16.1
Recreation:
/tp @s 29999950 100 29999950
/locate mansion
/tp @s 30001184 ~ 30001472
>> Invalid location to teleport
Hi there!
This looks like a duplicate of MC-126611. This is an intentional feature, and you shouldn't expect it to be patched as a bug. You can suggest a change to this on the feedback website at https://feedback.minecraft.net/hc/en-us.