It seems most of the packages in AUR don't support ARM compilation, therefore id rather not have to wait for download and compilation start to find out that the package isn't supporting ARM.
I don't think that's feasable.
The only way Pamac can know if a package is supported on ARM or not, is to look through each package PKGBUILD. AUR has thousands of packages.
As far as I know, there is no AUR API that can be used to filter in architectures.
If you are downloading and trying to install the AUR packages to see if they will install, you're using the AUR wrong. The AUR a assumes you know what you're installing and from where. Just clicking on an app icon in Pamac and hitting the Build button is not a smart way to use the AUR. Eventually, you'll run into more serious problems than unsupported CPU architecture.
There is a reason why the AUR is disabled by default in Pamac.