Thanks for reaching out.
I will gladly assist you with your concerns.
What type of device are you using?
To set your default storage to your SD card: Go to device “Settings”, select “Storage”. Select your "SD Card", tap the “three-dot menu“ (top-right), now select “Settings” from in there. Now select “Format as internal”, and then “Erase & Format”. Your SD Card will now be formatted as internal storage.
Unfortunately, the photos that are being saved to your SD card can't be backed up to Samsung Cloud. Only the phone internal storage can be backed up that way.
I have an S10 plus. What's the point in having expandable storage if it can't be backed up? Most people now stream music instead of download it and almost everyone uses a cloud service to back up their photos. I don't trust a removable SD card to keep my memories safe without backup. Sorry.