This is also a problem for ARM servers. Oracle's free tier is quite generous, especially if you use their free ARM offering (4 * 1 core with 6GB of RAM, no time limit on the free offering), but you can't run Mailcow on it.

This has been flagged on Github and the dev's response was "well, don't run anything important on a free server" and that was basically the end of that. I was pretty disappointed with that, but on the other hand there's nothing that prevents you from building the images yourself on ARM.