That a good question and its variable, I'm not a camera buff, yet the faster the bit rate the better the video quality and the larger the video file to record / transfer. For standard 4K V30 A2 card works well, yet V60 or V90 card may be a better choice. V30 means writes at 30MB/s minimum,,, V90 writes at 90MB/s minimum, For 4K @ 60fps on one drone I fly, I use Samsung Pro V30 A2 and the video looks fine, A2 is higher performance than A1. I'm considering moving up to V60 or V90 card myself and test the difference.
Go for V60 micro sd card or V90.
ADATA Premier One V90 64GB 4K, 8K Ultra HD and 3D/VR--- $34.03 on Amazon.