The widepeepoHappy emote is used to express boundless joy or great happiness. While the peepoHappy emote is used to express happiness, widepeepoHappy goes a step further. It is the intensified form of peepoHappy and is meant to express much more joy and happiness. Basically, the emote can be considered as a counterpart to widepeepoSad.
Like MonkaS or PepeLaugh, widepeepoHappy comes from the family of "Pepe The Frog" emotes. These emotes are based on comics by Matt Furie and have their origin in the imageboard 4chan. To use widepeepoHappy, you have to resort to the common browser extensions, as it is not part of the Global Emotes on Twitch.
Nevertheless, like so many Pepe emotes, it is an integral part of Twitch culture and is one of the 50 most popular emotes on FFZ (February 2022).