[FROG] Route Server Functionality

I’m trying to better understand route server functionality on FRR (7.5.1 specifically) and how it differs from quagga. I found the commit in which the legacy quagga special-case code was removed and replaced by the use of add-path. What happens if the route server and the client are unable to negotiate add-path as required? If the legacy code were still in place, I would expect a failover to it in that situation. Since the legacy code is no longer present, is the client required to have properly configured add-path in order to properly talk to the route server? Thanks, Michael