I entered:
WordPress address (URL): https://myhost.dyndns.org/wp
Site address (URL): https://myhost.dyndns.org
By changing the Site address as I’ve done here, as I removed the “/wp”, it makes me able to see the main page from a PC on my LAN, but not login, as I mentioned. If I keep the default settings, with Site address same as WordPress address, it makes me unable to reach even the main page from a PC on the LAN.