Uses Title::getNextRevisionId and Title::getPreviousRevisionId, both hard deprecated
I guess the logic to get to them isn't executed in the course of every-day editing, so it wasn't noticed? By manually manipulating my url to
https://meta.wikimedia.org/w/index.php?title=User:DannyS712/Global_watchlist/Updates&diff=21140244&oldid=21135074&direction=next and
https://meta.wikimedia.org/w/index.php?title=User:DannyS712/Global_watchlist/Updates&diff=21140244&oldid=21135074&direction=prev triggered the deprecations
[YEqxJXgkpBWUf0W1SfI6IQAAAEQ] /w/index.php?title=User:DannyS712/Global_watchlist/Updates&diff=21140244&oldid=21135074&direction=next ErrorException: Use of Title::getNextRevisionID was deprecated in MediaWiki 1.34. [Called from MediaWiki\MassMessage\MassMessageHooks::onSkinTemplateNavigation]
[YEqxcq4x0sbnZX2Y4WJR0gAAAM4] /w/index.php?title=User:DannyS712/Global_watchlist/Updates&diff=21140244&oldid=21135074&direction=prev ErrorException: Use of Title::getPreviousRevisionID was deprecated in MediaWiki 1.34. [Called from MediaWiki\MassMessage\MassMessageHooks::onSkinTemplateNavigation]