Filter to check for more than one instance of a track number from 1-9 in each folder?

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2

Again:
Mp3tag knows nothing about the content of folders.
It handles track by track.

You can load the content of a folder and sort by TRACK number.
Then you can SEE if there are more then one track with the same number.
But you can not compare multiple tracks or folders or albums.

You can only manipulate one track after the other.