It is no longer experimental, because the latest version is "22.0" instead of "0.22.0", the leading zero is missing 
The version number is not an indicator of experimental or beta status.Bitcoin Core still (intentionally) contains a line that says "this software is experimental". The line saying that Bitcoin Core is beta software was removed in 2014.
Is there an announcement for this anywhere? I don't think the release notes of 22.0 included anything about this numbering change. 
It is a cosmetic change and does not indicate anything of significance, so there was no announcement or celebration because there is nothing to announce or celebrate.