I'm just an Arch user and not an expert but AFAIK it's not officially supported (by Arch's packaging system). One is encouraged to update the entire system before installing anything new. If you installed just MyCoolCalculator vLatest and it pulled in the update for ImportantWidelyUsedDependencyX, dependent apps could potentially/do break, because multiple versions of that dependency are not kept. At least AFAICT.
The AUR is said to provide options for non-latest software, and I guess you have options like Flatpak too.
The AUR is said to provide options for non-latest software, and I guess you have options like Flatpak too.