Anyone have an answer on this topic, why garde la damme (when the queen was attacked) and the "check" warning have largely been abandoned in serious chess?   When did warning the player fall out of fashion?  Thanks.

Hmmz, I never said Garde la Damme, but I still say check :) Most of the time with a big irritating smile on my face :D

In my entire chess lifetime I only knew one player who said "garde" when threatening the queen; this was casual play.  So I never knew it was a custom elsewhere.

If your definition of "serious chess" includes rated OTB play, probably the most logical reason for not announcing check verbally is that talking during the game is discouraged if not actually contrary to the laws of tournament chess.

If one is playing "serious" chess, then he probably already knows he's in check.  Calling out check is redundant and only useful for beginners

Well my brother in law insists that i say garde but i always say check but anywho my brother in law annoys me he still uses descriptive notation as well becasue we were playing a game and i said damn i dont wanna play d5 and he was like wtf is d5

I always say, "Your Lady" and "Check" OTB.  Very satisfying.