That's what many Samsungs do. The card is as you guessed integrated into the Samsung phone. For now this is a Samsung thing. I haven't encountered it on any other phone.
In file manager it is showing Internal SD card.
I did not add any SD card in my phone.
I am curious: do all or most mobile phone have SD card integrated as
a disk?
If mobile phone stops working, is it possible to save the data from that integrated SD card?

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