Which key slot is used by `onlykey-agent`?

For generated keys, the documentation said that a random key is generated to generate an unlimited number of identities, so which key slot is actually used? Will onlykey-agent break previously imported PGP keys?

A key slot that is reserved is used. No onlykey-agent will not break anything previously used, the app must be used to load or change keys.

Thanks for replying. Is there any way to kind of re-generate or reset the reserved key slot for onlykey-agent?

You could reset the OnlyKey, upon setup a random key is generated.