I would like to confirm this still happens on 1.16.201
I would also like to clarify that if you switch to "Load" mode BEFORE typing the structure name, then it actually works as expected. Unfortunately, the default mode is "Save", which causes this problem to happen often, even when you know the problem exists...
If the fix will take long, then a quick partial solution could be to just change the default mode to "Load" (or even a "Please Select a Mode" default option), so the user has to deliberately change to "Save", and reduce the chance of this problem happening. Alternatively or additionally, have an overwrite confirmation dialog for any existing structures.
Why is this resolved? I tried those 3 steps, but still fails with: "Something happened on our end." in the store.
The "check for updates" button in the Windows Xbox app doesn't even attempt to do anything.
The "Update" button in the Minecraft Launcher starts an update attempt, then either stalls (need to close launcher), or fails, and then can just Play as 1.20.73.