Word for undervaluing or ‘one upping’ someone else’s achievements

I’m in a community where theres a lot of people who share a milestone/achievement or difficult experience, that is almost always followed by someone who goes “yea well I achieved X”, so as to undermine(?) the other.

The urban dictionary definition of “one upper” is pretty much it but I'm looking for a more appropriate word

One-upping is the common phrase for putting down another's achievement.

The practice of One-upmanship is longstanding and much more subtle than just saying out loud what you did to top the other's victories. https://www.amazon.com/One-Upmanship-Stephen-Potter/dp/1258783339