I think you still have to specify the URL up to the greader.php page, maybe in your case it would be

https://freshrss.example.com/api/greader.php

Turning it on by default would be a massive disservice to the work that domain registries and registrars have been doing to allow Unicode to be used in domain names. In Spanish speaking countries the ñ character is pretty ubiquitous for example, and the workaround of replacing it with an n creates many problems like misdirected web traffic and typos in email addresses. Unicode in URLs and domain names is a feature, abuse should be attacked by means other than disabling it.