Hi @elihelou,
Welcome to the Community!
Thanks for reaching out 
The reason you are not able to map these fields is that the system can’t map two drop-down fields (more on this here). This is due to a limitation of our data sync integration engine, so it won’t work on any data sync integration.
You can see which mapping possibilities are possible here.
As a workaround, you can map a drop-down field towards a single text field but it will be restricted to a single direction sync (from drop-down to a single text field).
@FransLeys, do you have any suggested workarounds or insights into the roadmap? Thank you!
Best,
Kristen