I think the VM has to be switched off, not just suspended for the arguments to be editable. There are also some flags that UTM insists on and won't let you remo

I think the VM has to be switched off, not just suspended for the arguments to be editable. There are also some flags that UTM insists on and won't let you remove, which actually seems kind of reasonable - QEMU is really low-level and it's possible to run it in modes where UTM won't be able to connect to it.