If you use trininja telegram notifier, do you get notified if your former username is mentioned in the forum?
It is about those bots, from third-party developers, not from forum so it does not belong to Meta.
Forum members can notice changes and know about username changes by themselves. Officially notify about it is not encouraged.
Why are you guys posting the old names of people who clearly needed their names changed for privacy reasons? Obviously any data posted online is going to be quickly archived somewhere, but that doesn't mean that your highlighting/reposting of it has no effect. In some cases you may literally be putting lives in danger. If you were investigating a scam or something, that'd be different, but you seem to just be indiscriminately & recklessly dredging up data that would best be forgotten.