Confirmed that linux-hwe-5.4/5.4.0-89.100~18.04.1 kernel in -proposed built the vbox_* modules from virtualbox-guest-dkms_6.1.22-dfsg-2~ubuntu1.20.04.1_all.deb, which restored the behavior as expected.
Confirmed that linux-hwe- 5.4/5.4. 0-89.100~ 18.04.1 kernel in -proposed built the vbox_* modules from virtualbox- guest-dkms_ 6.1.22- dfsg-2~ ubuntu1. 20.04.1_ all.deb, which restored the behavior as expected.