So either Shelly is disobeying your pacman.conf or something in there is misconfigured.
Or I’m misunderstanding how repository priority works. As far as I know, if a package is present in two or more repositories, then the package from the highest repo in your pacman.conf should be installed regardless of version number. In which case, your v3 capable processor should prioritize cachyos-extra-v3.
Might as well take a look inside your /etc/pacman.conf to make sure everything is good.