I will have the warning later. It's Hugo, not ox-hugo
As you figured out, the RSSLink deprecation is from Hugo itself.. You probably found out the release notes where that was announced.
Regarding tagging ox-hugo, I don't think #Mastodon supports hyphens in tags, because the whole "ox-hugo" does not hyperlink when prefixed with "#".
Instead try #oxHugo next time (no hyphens but yes camelCase).
This Mastodon instance is for people interested in technology. Discussions aren't limited to technology, because tech folks shouldn't be limited to technology either!