Orange Pi Zero 3: max write speed 20MB/sec?

I have been trying with multiple SD cards, including a Sandisk Extreme (rated at 90MB/sec in writing speed) and I am only getting 20MB to 24MB/sec with the OPi Zero 3.

Is that a limitation of the SD reader on the board?

I am assuming it's not the network, as I could write at around 45MB/sec to a ramdisk, via an ethernet connection.