DeletedUser24 Charging-only when locked
Although I don't have experience with an Onlykey, it sounds like the OP wants to use it as a USB peripheral? "Charging-only when locked" will not allow USB peripherals when locked; it only allows charging. From the feature description in the settings menu:
Turns off all non-charging USB-C port functionality.
So if we are talking about connecting a USB peripheral in BFU mode, then the setting "Charging-only when locked, except before first unlock" will do fine.