Earlier I mentioned that the Season 1 finale of Stargirl was “essentially” the live action debut of The Shade (after several animated appearances), and I used that word because it was, specifically, the first time the the more definitive iteration of the character was used in the medium.
Granted, that episode is heavily influenced by the effects of the (Grant Gustin) Flashpoint Paradox from the beginning of season and Stargirl’s ties into the Arrowverse continuity are still very loose at the moment, so introducing the more traditional version of The Shade now does not break too many rules.
However, the Arrowverse sort of tackled the character first on a Season 3 episode of The Flash, which depicts him as a nameless man (played by Mike McLeod) who can vibrate his body enough to project himself as a large, shadow-like creature – unless you have a crap-ton of light to shine on him.