ADB can be used to disable it without GrapheneOS by disabling the packages providing the high level implementation of wireless emergency alerts. It's not something most people can be expected to do though. It's actually a lot easier to install GrapheneOS via the web installer than using the CLI ADB shell. ADB is also quite dangerous and people can be tricked into giving very invasive access to malware with it. We're not recommending that people use ADB for this but rather just noting it can be done.