How to install virtualbox-ext-oracle?

Due to differences between Manjaro unstable and stable branch - to use AUR - it is almost mandatory to use testing or unstable branch.

To educate yourself on use of AUR please jump to article About Manjaro and AUR

You don’t need the extensions unless you have very specific requirements.

Your issue is because AUR expects Arch package level - you are likely using stable and therefore the version discrepancy.

Switch to unstable

sudo pacman-mirrors -aS unstable && sudo pacman -Syyu
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