The receiver c534 is different from a Unifying receiver in several ways. It can only pair with some keyboards and mice. It can only pair with 2 (or 1, for some receivers) devices. It can only perform a limited number of pairings. It cannot unpair. Pairing replaces a previously paired device of the same kind. Its serial number is in a different place - maybe, this change needs to be checked. Will Logitech confirm?
This pull request improves handling of c534 and other non-Unifying receivers. This pull request addresses Issues https://github.com/pwr-Solaar/Solaar/issues/598 and https://github.com/pwr-Solaar/Solaar/issues/579