https://www.guidelive.com/video-gam...32gb-microsd-cards-on-the-new-nintendo-3ds-xl
You can use Minitool Partition Wizard Free version to re partition the SD card, for the card you have to Partition it FAT32, 32Kb cluster and set the partition to Primary Partition, not logical, since you used emunand in the 4GB card, what you can do is figure out which folder inside the "Nintendo 3DS" is the emunand, and which one is Sysnand, easy way is just to delete all of the folder inside the "Nintendo 3DS" folder and re set up the system, and
https://3ds.hacks.guide/finalizing-setup
On the B9S thing if you have a boot.firm file on the root of the SD card, then you are on B9S, if else you are on A9LH