How can I remove the command line messages during boot and shutdown on my Arch Linux?

You can edit the `/etc/default/grub` file to change the boot messages. Uncomment the `GRUB_CMDLINE_LINUX_DEFAULT` line and add `quiet` or a specific log level like `loglevel=4`. After that, run `sudo update-grub` to apply the changes. Just a heads up, keeping some logs can be super helpful if your system runs into problems while starting or shutting down.

Check out the Arch Wiki for ways to achieve a silent boot. They have specific instructions for configuring `plymouth` and handling the boot parameters. Here are the links to the relevant pages: [Silent boot](https://wiki.archlinux.org/title/Silent_boot) and [Plymouth](https://wiki.archlinux.org/title/Plymouth). They should be really helpful!

Have you tried using `plymouth`? It's a service that many distributions use to hide boot messages. If you're not seeing it working, make sure it’s properly configured, especially since you disabled grub. It might help to clarify what you exactly mean by that to get more tailored advice.