By the way, it’s certainly possible to add additional language keyboards from Settings - Region & Language. That makes it possible to use a non-Terminal-style keyboard again.
But oddly, adding English (UK) or English (Canada) doesn’t effect a change to non-Terminal-style, while adding French, for example, does. I guess my modified English (US)+ Terminal keys prevents that.
EDIT: You can also have more than one personal .yaml in .local/share/squeekboard/keyboards and switch between them. If you have, say, both us.yaml and fr.yaml, and your region/lanuage is set to English-US, the following happens:
. Keyboard defaults to terminal style, but English (US) is shown as selected when you tap the globe icon.
. It’s not possible to see/use the original non-terminal-style English (US) keyboard.
. Selecting French displays a non-terminal-style keyboard in French layout.
. Then selecting Terminal displays the terminal-style keyboard with French layout.
In case anyone is wondering, if you change the personal us.yaml (in .local/share/squeekboard/keyboards) to terminal.yaml, it doesn’t help; the regular/original keyboard behavior takes over again, i.e. it doesn’t default to terminal-style everywhere anymore. The personal terminal.yaml is ignored.