Today I installed my first custom ROM (Lineage OS 17.1, official page) on my old Motorola phone (Moto G3 Turbo edition, XT1516). Everything great until I wanted to format my SD card as internal storage, you know, that kind of format android uses that doesn't allow you to view its contents if you plug it on a PC. Well... at the moment to configure it, it asks me if I want to format the SD card, if I select format SD card it formats as portable storage as default (screenshots in Spanish).
And to get that menu again I need to remove the SD card from the phone, erase the partition and try again. I can exit that pop up menu touching another part of the screen. This time it shows me two options, first, additional storage (Almacenamiento adicional in Spanish) which is only for apps, etc and to use it only on the phone, the second one is portable storage, the one I don't want. The problem is the first option is disabled!!, what am I doing wrong? If I insert the SD card already formatted as FAT32 the configuration menu doesn't appear and uses it as portable storage.