Go to blissos.org → Downloads → Select "Bliss OS 15" (Android 12L) → Choose the .ISO file (yes, Bliss actually provides an ISO, because it uses a custom x86 kernel). This is likely the file you are looking for.
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In VirtualBox, go to VM Settings → Network → Adapter 1 → Attached to: NAT (not Bridged). Android 12 has trouble with Bridged mode. Go to blissos
