You're on linux, the Chrome OS Recovery Utility isn't supported, but you'd still want to try Chrome OS Flex? Worry no more!
(NOTE: I'm aware of Googles offical Linux script, but that one is "in maintaince mode" and also doesn't have flex)
Install the following packages: jq, curl, wget, unzip (most, if not all, should be preinstalled)
Then run the script
curl -Ls https://gist.githubusercontent.com/mkg20001/ad3fd73ee0224aa63ff85a331227a264/raw/213bf1b06d45107dbf65b97a0e1a8d9584341fcb/downloader.sh | bash -
It'll do it's job.
Afterwards flash the .bin file to some flash drive.
sudo dd if=*.bin of=/dev/sdX oflag=direct bs=16M # replace X with your target device
QEMU doesn't want to work so far, so just try on some real hardware.