You can install MongoDB from the “bullseye” (Debian 11) repository on Debian 12, but you’ll need to also add bullseye to your sources.list to get the libssl1.1 package on which it depends (Debian 12 provides libssl3 which is not ABI-compatible with libssl1.1). It’s a bit hackish but it does work well in my own tests (and is simpler than recompiling or going through a container).
But I do hope we’ll get pre-compiled binaries for Debian 12 (“bookworm”) soon enough so we don’t have to do those kind of tricks.