When someone sends you several messages in a DM, only the first unread one plays Discord's in-app message sound.
Read the DM and the next message pings again.
Banners and badges still show for every message; only the sound is held back.
Server channels are never affected.
A port of Vencord's OnePingPerDM.
Settings
DMs to affect picks Both, User DMs or Group DMs. Both by default.
Allow Mentions plays the sound for every message that mentions you. Off by default.
Allow @everyone plays the sound for every @everyone and @here in group DMs. Off by default.
Limits
It works while Discord is open. Push notifications that arrive while Discord is closed or in the background come from Discord's servers and the system, so they still ping for every message.