A portable card is a memory card like any other. The phone writes an exFAT or FAT32 file system to it, puts photographs and video in DCIM, lets WhatsApp and other apps keep their media in folders of their own, and reads it back the way a camera or a computer would. When the phone reboots mid-write, when the card is pulled, when the card wears out and errors, the tables tear and the phone reports the card corrupted and offers to reformat it. The reformat rewrites the tables and starts again; the data behind them was intact until that moment. Refuse it, take the card out, and the bench rebuilds the tables on an image and carves what the tables no longer point at.
An adopted card is different in kind. Android formats it with ext4 or f2fs, encrypts it with a per-device key, and from then on treats it as part of the phone's own storage, moving apps and their data onto it. The design is meant to stop a card being taken out of one phone and read in another, and the documentation says so plainly: the keys should not be extractable from the parent device, and the storage device cannot be mounted elsewhere. An early analysis of the first version found the key in a file on the phone's own data partition, which is destroyed by a factory reset. The consequences follow. If the phone is alive and the card is merely corrupted, the phone itself is the only tool that can read it, and its own migrate-data option is the way off. If the phone is dead, reset or gone, the card's contents are ciphertext without a key, and no laboratory on earth has a way round that.
Telling the two apart takes a minute. On the phone, Settings and then Storage lists the card as portable or as internal, or shows the option to format it as the other. Off the phone, a portable card shows an exFAT or FAT32 volume in a computer, with folders; an adopted card shows a partition a computer cannot read and no file system it recognises. Unsupported SD card, as a message, usually means the second kind arriving in a phone that did not adopt it, or a file system the phone does not read; it also appears for a card that has failed.
The remaining case is the card itself. A portable card the phone cannot see at all, or that shows 0 bytes or the wrong size in a computer, has a failed controller, and is monolith work like any microSD. The free look says which, before anything is charged.