The current version of BalenaEtcher, needed to flash SDs on OSX only supports OSX 10.10.++
If you need to use BalenaEtcher under OSX 10.9.5, then use version 1.5.63.
https://github.com/balena-io/etcher/releases/tag/v1.5.63
Typically again there is no info regarding this on the BalenaEtcher website, not to speak of a simple prominent tab labelled "system requirements", and one needs to be aware of Etcher using Elektron, which makes it an application requiring stupidly high amounts of RAM and disk space, although this only has one button and three steps to perform. Modern devs seem to be spoiled regarding tech ressources.
Anyhow... i'll stop my rant now and you'll hopefully *enjoy this info 😉
P.S.: Obviously you may flash SD card using command line: https://learn.bela.io/using-bela/bela-techniques/managing-your-sd-card/#flash-an-sd-card-using-the-command-line