When .o extension will be added?

Hello.
Subj please.
Thank you.

You mean as a Top Level Domain (TLD)?

I don’t think there’s such a thing. Or any other that’s a single letter.

http://data.iana.org/TLD/tlds-alpha-by-domain.txt

It’s an OpenNIC TLD: https://wiki.opennic.org/opennic/dot

As far as I’m aware, Cloudflare doesn’t support alternative roots/name systems.