Blocked port on orbi RBR10 router and network that needs opening?

> [...] my Daikin aircon wif adapter [...]

   Not a very detailed description of anything.  Does the maker provide
any instructions for it, whatever it might be?

> Both my orbi based at home wifi network and my Daikin adapter unit
> both show as available networks on my phone when I am at home but I can
> only operate one of them at a time. I cannot couple them.

   Which radio band does your (unspecified) "my Daikin adapter unit"
use?

   "cannot" is not a useful problem description.  It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> If I ask my Daikin adapter unit to search for available wifis to
> connect to it cannot see my orbi based home wifi network even though it
> is obviously an available network to my phone.

   That sounds like a problem.  Does it "see" any other SSIDs?

> My Daikin 5G adapter [...]

   "5G"?

> I wonder if there might be a blocked port on the orbi system on one
> side or the other that the Daikin adapter needs access to?

   Ports matter _after_ you get a device connected, not before.

   Many Internet-of-Junk devices can use only the 2.4GHz radio band.
Many mobile apps which are used to configure (and manage) these IoJ
devices require that the mobile device also be using that band, at least
during the configuration process.  With the simplified (that is,
limited-flexibility) wireless controls of Orbi routers, arranging that
can be difficult.