Hi, what image are you flashing onto the SD card? Etcher flashes that image exactly, and doesn’t affect your card’s size.
What likely happens, is that the image has partitions that are formatted with a file system which macOS cannot read natively. For example if you are flashing a balenaOS image, there the first partition is a FAT32 partition with about that much size, while, the rest are
ext4 partitions, and I think you would see behaviour similar to this, if your system cannot read
ext4 file system. You can try to plug the SD card into a Linux machine, or try to erase the partitions on the card currently to check (and then reflash later on), for example following these hints https://github.com/balena-io/etcher/blob/master/docs/USER-DOCUMENTATION.md#recovering-broken-drives
Let us know how it goes, and rest assured, your SD card capacity does not change by flashing it with Etcher.