Moving from Debian 12 to 13 I faced the same problem.
My readings told me it’s because the newer kernel loads and inits kvm module by default, whereas the previous version did not. This makes impossible for Virtualbox to init virtualization on its own, so the sulotion is either to disable kvm initialization in GRUB adding a kernel parameter ( kvm.enable_virt_at_load=0 ) , or blacklist kvm module via /etc/modprobe.d/something.conf.
I choosed the latter, this what how it looks now on my computers:
cat /etc/modprobe.d/kvm-blacklist.conf
blacklist kvm_intel
Adding that, and rebooting made Virtualbox working flawlessly.
As for version, I have now Virtualbox 7.2, is there a reason you are still trying 7.1?