WiFi problems with DNS.adguard.com

At home I can use the AdGuard DNS via settings -> WiFi & network -> private DNS -> private DNS provider hostname, and setting that hostname to dns.adguard.com. In many public places where I do have WiFi without using this DNS, using AdGuard gives the error "Private DNS server cannot be accessed" and WiFi is not used. Specifically the EduRoam university network does not work with the AdGuard DNS. It means I often switch back to private DNS -> automatic, but in practice that seems to work the same as private DNS -> off: even at home where the AdGuard DNS would work, it is not being used. Does anyone know if there's another setting that would make AdGuard usable in those public places, or at least to have an "automatic" option that does at least use AdGuard when possible?