Force compagnon app to use local address / what is HA IPv6 local link IP?

My HA is on a 192.168.5.0 subnet (VLAN) which is IPv4 only.

My clients are in the main LAN (IPv6 + IPv4), so it’s can only talk to home assistant using IPv4 when connected in my lan).

In Home assistant companion app, I have my internal URL set to https://192.168.5.55:8443

and my external set to https//my.subdomain.com

However, it’s seems like the app only try to connect to my external address (which can’t work in my LAN as it’s using my IPv6 adress)

how can I force the app to connect with my local link IP when am in my local network – or is that impossible because my subnet is different?

if so how can I tell what my HA IPv6 local only IP is ? (so I can route the traffic main LAN IPv6 to HA VLAN IPv6 Local only