[rsfinn]

(Straying a little off topic to provide the following hint:)

There's a setting for this in System Preferences > Keyboard > Keyboard. My recollection is that this was previously a checkbox that toggled the "double-Fn to invoke Siri" function on and off, but as of Big Sur (at least) this is now a popup menu control, where the choices are "Change Input Source", "Show Emoji & Symbols", "Start Dictation (Press Fn Twice)", and "Do Nothing".

My test M1 machine was set up from scratch last year (i.e. no account migration) and has "Do Nothing" selected here, so I can't confirm that "Change Input Source" is the default for new users, but its position as the first item on the menu is suggestive.