selfhost.eu offers dynamic DNS which works perfectly fine with my router, using their API access as documented by them. It also works perfectly well with Let’s Encrypt integrated in Nginx Proxy Manager.

• can handle .at domains
• is not Cloudflare
• is registrar and name server
• is European (Germany)
• supports Nginx Proxy Manager

They’re in the market since 2001, I use them since ca. 2010 and never had any issues. Their website looks ancient, almost historic. But it’s functional.