Some packages may require older versions in which case multiple versions will have to be kept installed to allow those apps to work. That concerns not only AUR packages but also apps in the official community repos, so be careful to remove ‘double’ installs.
Offroad, for example, won’t work unless a java version below 12 is installed with:
sudo pacman -S jre11-openjdk jre11-openjdk-headless
PATH="/usr/lib/jvm/java-11-openjdk/bin/:$PATH" offroad