I’m considering doing this, making a standalone from the template. Some of the qubes packages failed to install even with the “fix” of switching the sources.list to trixie from bookworm. vm-recommends and one of the qubes-networkmanager packages. I’m not sure what the effect of that is at this point.
Also I’m noticing a number of other posts having the same problem with qubes-core-agent breaking the install. None of them got a satisfactory response, so I’m thinking there is a larger issue here, which is why I asked the question Can qubes-core-agent be used in a standalone at all or is that not a compatible use case?