Mavic Air 2 has max video bitrate of 120 Mbps, which translates to 15 MB/s. Meaning, any V30 and higher rated SD card (preferable SanDisk Extreme), will be more than enough. Don't buy biggest one available (Air 2 will accept cards up to 256 GB), but rather few smaller ones (64 GB, for example) in case of failure and possible data loss. Try to exchange cards on every battery swap.