Look, this is beyond a longshot, but Reddit claims to have it, Return to Monkey Island’s release date: September 1st.
Take this with a BIG PINCH OF SALT: in Devolver Digital official website, the code of the page for Return to Monkey Island contains a block of structured data with information on the game.
There are two date "keys":
"date_override" : "Coming 2022" (which is what appears in the page to users)
"date" : "2022-09-01T12:00:00.000Z"
The Redditor goes on to speculate that it’s a placeholder, which... is likely.
Mojo, meanwhile, generally leans toward the more plausible Talk Like a Pirate Day: September 19th.
Update! A quick scan of a couple of Devolver's other upcoming games suggests they default to the first of the (presumed) release month. E.g. Skate Story has April 1st, 2023 set as "date" and "date_override" to "Coming 2023." Reigns: Three Kingdoms' "date" is December 1st, 2022 and "date_override" is "Coming 2022."