We have a duplicated menu in antiX as well.
Specifying all of the submenu (<menu></menu>) blocks in the
applications.menu file as <Menuname>Block Name</Menuname> instead of relying on
<Merge type=*.... stops the duplication.
It seems as though this is an upstream bug from pyxdg almost 2 years
ago.
Reported issue
https://gitlab.freedesktop.org/xdg/pyxdg/-/issues/11
Merge request / suggested changes.
https://gitlab.freedesktop.org/tmccombs/pyxdg/-/commit/087410c64fd4d6db1ec2d70aa196e69b25c887eb
