You can find it on various Flash game preservation archives (like Flashpoint) or via dedicated Discord servers that host the Ultra Plus mod. Be wary of dodgy .exe files; the game originally ran in a browser, but the 2022 version is often repackaged into a standalone Flash projector.
While SNK released KOF XV to critical acclaim, a separate community of modders and Flash enthusiasts kept the spirit of 2D sprite fighters alive in a browser window. If you ever get the chance to play it, pick Mario, spam fireballs, and watch as Iori Yagami gets flattened by a blue shell. That is the Wing experience. The King Of Fighters Wing 5.5 Ultra Plus 2022
The full title——indicates it is a modded or updated version of the original Wing 5.5 (released around 2016-2018), patched unofficially by community members to include characters and balances as recent as 2022. The Roster: Chaos Theory The hallmark of Wing 5.5 Ultra Plus is its roster. Official KOF titles average 30-50 characters. This fan game features over 100 characters , but not just KOF characters. You can find it on various Flash game