Macbook Pro - install operating system on SD card?
Short answer: Yes, but it will not be ideal

Long answer:
Yes, it is possible to install macOS onto a SD card, but SD card have low read/write speed (unless you get one of the SDXC II card which can get 280MB/s which is still pretty slow for daily use, and they are expensive, cheap ones won't do anything in speed) my SSD can get around 465MB a second, and that is not the best SSD. So make sure you don't care about being slow with installing OS into them. Also by the way you can't really make large amount of writing into it or else it will break: they are not designed to have a system installed onto it.