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YouTube disabled SRV3 subtitle uploads and started deleting them on existing videos
(piunikaweb.com)
This is a most excellent place for technology news and articles.
More like unofficially supported. The fact that they worked points to the fact that they were quite literally supported.
Unsupported typically just means they wont provide (technical) support if/when it breaks.
Generally unsupported means "we will not provide support for this, you're on your own if something goes wrong"
Rather than "this will not work at all, we have ensured that"