Gnome boxes ....device not bootable

hello everyone I just registered. I have a problem with gnome boxes I read almost everything on the subject, but unfortunately I did not solve it.
As per the title I find myself with an error “no bootable device”. Given that I have been using boxes for a while now, as I need to use photoshop (the publisher for which I work wants the .psd files)…In these days I had decided to install to try it “startOS”, unfortunately after downloading the .iso and set the virtual machine I am with the described error…can you help me, thank you for taking the time