The previous thread is relevant since it includes details of your setup. The upshot is that you device isn’t Roon Read, and therefore can only use Airplay.
Roon will see an Airplay device under Settings > Audio, and this should be enabled before use. Roon does not require a PIN to use Airplay.
However, from the previous thread, it seems that you first need to setup the Pearl to use Airplay. Please see the post by @BlackJack.