You can install an older version of an AUR package by doing the following:
https://forum.manjaro.org/t/build-package-from-specific-commit/69062/2?u=yochanan
The commit you need can be obtained by clicking View Changes under Package Actions on the AUR page, click the commit message you want, then copy the commit hash.
Tip: In the future, never update virtualbox-ext-oracle until the matching VirtualBox packages come along.