Describe the issue
Custom arguments cannot be specified in JSON format because UTM eats the quotes

Configuration

• UTM Version: 4.5.2
• macOS Version: 14.4.1
• Mac Chip (Intel, M1, ...): M1 Pro

Try to specify any custom JSON arguments such as

-blockdev
{"driver":"file","filename":"/Users/nick/Library/Containers/com.utmapp.UTM/Data/Documents/Debian loong64.utm/Data/edk2-loongarch64-vars.fd","node-name":"libvirt-pflash0-storage","auto-read-only":false,"discard":"unmap"}
-blockdev
{"node-name":"libvirt-pflash0-format","read-only":false,"driver":"raw","file":"libvirt-pflash0-storage"}

It will not work because UTM eats the quotes, with the json malformed error message suggesting that the quotes have been eaten.