After doing some tests with Anton it does look like the connection is deliberately blocked.
Connection(s) during day, works.
Wired connection from home, Quest 2, DeoVR, evening, doesn't work.
Mobile connection but with same ISP, Android, DeoVR, evening, doesn't work.
VPN, same devices, works.
About half the routing to the SLR servers he has is the same as mine, I have no issues (other ISP).
I was setting up a VPN server so we could try him connecting through my connection, and now my firewall is all messed up 😢 Nothing of inbound protocols work any more, FTP, DLNA, HTTP ... sigh