Arch has changed the location of where the cert files should go to: /etc/ca-certificates/trust-source/anchors If you follow the instructions for the certs but move them to this dir and run: sudo trust extract-compat you should be good to go.
Ref Links:
Arch Wiki: https://archlinux.org/news/ca-certificates-update/
Article found for certs: https://unix.stackexchange.com/questions/373492/installing-certificates-on-arch