You need Monterey firmware only. You can just do a side install once (to update your system firmware, which needs to be at least as new as the newest OS bundle)

You need Monterey firmware only. You can just do a side install once (to update your system firmware, which needs to be at least as new as the newest OS bundle) into another volume, nuke it, then install Asahi with the Monterey firmware bundle option, and keep your main macOS install at whatever version you want.