I've not been able to reliably install on anything other than #NixOS, so you've got nothing useful from me. Maybe you could try Nixpkgs on Arch, but you probably want native Arch packages?
Discussion
Yeah, thanks for the suggestion. I am not proficient in the #arch way yet. I found a very useful and thorough video on YouTube (https://www.youtube.com/watch?v=SX1JHWViI7E). Unfortunately, it was made 4 years ago and I cannot follow through. There are some differences between #php7 & #php8, which I cannot fully grasp.