vrit-install appears to not support installing off a Debian mini.iso:

Starting install...
ERROR    Couldn't find kernel for install tree.
Domain installation does not appear to have been successful.


The following patch makes that work:
--- ./urldetect.py      2022-01-26 19:25:19.835922099 +0000
+++ /usr/share/virt-manager/virtinst/install/urldetect.py       2022-01-26 19:25:22.447863479 +0000
@@ -751,7 +751,7 @@
             kpair = ("boot/linux_vm", "boot/root.bin")
         else:
             kpair = ("install/vmlinuz", "install/initrd.gz")
-        self._kernel_paths += [kpair]
+        self._kernel_paths += [kpair, ('/linux', '/initrd.gz')]
         return True

     def _detect_version(self):

Cheers,
-- 
                            |  .''`.       ** Debian **
      Peter Palfrader       | : :' :      The  universal
https://www.palfrader.org/ | `. `'      Operating System
                            |   `-    https://www.debian.org/