Mac storage basics · External storage and adding space
Can I use an SD card or USB flash drive for extra storage on my Mac?
Short answer: For occasional transfers, yes, but most SD cards and USB sticks are slow with many small files and less durable. A small external SSD is better for everyday extra storage.
For occasional transfers and small archives, yes. As permanent extra storage they're a weak choice: most SD cards and flash drives are much slower than an SSD (especially with many small files), wear out faster under heavy writing, and are easy to lose.
If you want space you can actually work from, a small external SSD is the better buy. Keep anything stored only on a card or stick backed up elsewhere.