Valve say it should just work, and there is virtually no control the game has over the Steam Overlay - the only API functionality is to ask to show the Steam Overlay (there isn't even a way for the game to ask to hide the overlay). The display and interactivity of the Steam Overlay is handled entirely by Steam which is made by Valve, so if you have any issues with it, you should contact Valve.
Sure, I'll contact Valve support.
Before that, just to confirm...
In the Steamwork Addon, I put the App ID of my game, the Overlay mode enabled and the Developer mode disabled.
and in my event sheet, at the moment the player will earn an achievement I put the Steamworks action [Unlock Achievement]
When exporting, I use the WebView2 option and send it directly to Steam..
I missing something?