Hi

Im not familiar with the standard duct sections in Cadmep but if you use the fabrication parts to draw the duct in cadmep and then to save to an maj file you just type 'createrevitmaj' the produced .maj file can then be opened in any fabrication program.

something else to try is typing 'revdesign' which will create a design line on selected ducts and this can then be automatically populated with fabrication parts if they are not already.

i regularly export revit parts to fab by way of exporting the graphic elements in to a rif file and then convert them in to fab parts within fabrication but i have never done this from cadmep

my only other comment would be that im still using 2021 versions as there is a lot of issues with 2023 last time i tried it and that may explain why things are not working correctly.

hopefully this will help

good luck