Please be aware that users with other phones than Fairphones shared the same experience according to the internet. It’s more of an issue with halfway recent Android versions, even if it was not a good idea technically from the very beginning.
Don’t let your SD card be formatted as Internal Storage. On any phone. Ever. Reasons are given in our sdcardguide, which @OldRoutard already linked to.
@urs_lesse … since you posted an /e/OS screenshot with how /e/OS addressed this issue here and since you tend to have access to the different Fairphones:
Do you know how current Fairphone OS on the Fairphone 3(+)/4/5 handles this in the meantime? Was a warning or something similar implemented?