Nope, you can use any SD card formatted to FAT32 with the 3DS. The system takes longer to boot with 128 GB, and minor issues appear with 256+GB (such as MenuHax not working), but other than that, it's fine from what I could read.
Thanks! So difficult to find accurate info on the web. I have a9lh and Luma and haven't noticed any boot-time difference from 64GB cards. I guess the difference might be fairly tiny, so that it could take a little longer, but it's still insignificant. Not noticed anyway. What I did find, though, was that connecting to the theme store won't work unless clusters are set to size 32. Just leaving that there for anyone who might come across that particular issue.

