I recently got a Galaxy A15 and I’m kinda new to more “modern” devices, after using pretty low-end devices. But I’ll keep this post pretty simple: what should I do to keep my data securely?
It all depends on encryption support. If the SD card is not adopted, the filesystem can only be read by Android in unencrypted status AFAIK. There is the option of adoptable storage, but I’m not sure if Samsung One UI supports FBE for adoptable storage. Internal storage might be a better choice considering that a bad actor needs to desolder the flash chip as opposed to simply pop out the SD card in order to bypass the phone’s storage controller. On the other hand, a SD card is easier to destroy physically than a whole phone.
I’d recommend not relying on Android’s FBE for super sensitive data and use VeraCrypt/Cryptomator.