Hi I came across exactly same problem. It seems the newly added VM you have one chance (only) to change the Chipset. The Q35 chipset seemingly not support any IDE bus. In order to boot Windows XP or unpatched Windows 7 you have to use the old i440fx chipset.

There are better explainations in this serverfault question How can I change qemu KVM machine architecture

I know it is kinda later and hopefully it could help other people. (This question seemingly the only one mentions Debian 10)

Hi I came across exactly same problem. It seems the newly added VM you have one chance (only) to change the Chipset. The Q35 chipset seemingly not support any IDE bus. In order to boot Windows XP or unpatched Windows 7 you have to use the old i440fx chipset.

There are better explainations in this serverfault question How can I change qemu KVM machine architecture

I know it is kinda late and hopefully it could help other people. (This question seemingly is the only one that mentions Debian 10)