Oh, seems they did exactly this, unfortunately: https://us.community.samsung.com/t5/Other-Mobile-Devices/format-Sdcard-as-internal-storage-on-A01/td-p/1295882.
The only solution then would be an alternative os, if available for your device, but only if the adoptable storage functionality is available there.
So far, I used to buy older, but higher class android phones at the same price you would pay for a more recent entry class phone, which always served me well. The drawback is that you are running out of (security) updates, but I do backup often, and I never had any issues anyway. However, I do not do critical stuff such as banking on the phone.