conversion from .kml to .pln or .flt files

[routeconverter]

I did not tried to minimize .kml files and I don´t know max size of the file could be imported to MSFS2020. I expected all .pln files could be imported, but I don´t know how to convert it.

I'm questioning the assumption that "all .pln files could be imported" when RouteConverter converted them from .kml files.

Why? Because .pln files contain, as @kumo found out, lots of information that isn't available in .kml files.

That why you (I don't have MSFS2020.) need to find out, what's minimally required. Then we can compare if that's contained in .kml files and if an implementation in RouteConverter makes sense since it will produce files that can be imported.

I hope that clarifies the typical process for a new file format?