If you want to block any top-level domain, just add it without a leading dot to your Denylist.

For example, if you want to block access to all websites in the RU domain zone, add ru to your Denylist.

Internationalized country code top-level domains should be added to the Denylist list in the IDN form: 中国 (Chinese IDN ccTLD), рф (Russian IDN ccTLD), etc.

A full list of top-level domains can be found on IANA website and Wikipedia.