I don't know of one that is totally stealth; it may be easier to hide / disguise the camera itself.
IIRC, the terms "transparent" and "black" are mutually exclusive in that if the cover was black, it'd be "opaque" and not transparent. There may be a "translucent" cover that is tinted but then it would not be totally stealth.
Perhaps you can share more info about what you're trying to achieve.
You've been on the forum for 4+ years, so you're aware most on this forum prefer bullet and turret (eyeball) cams.
I think at 20 meters no one is going to be able to figure out the camera is focused on them if they can even spot the camera to begin with. Too far away especially if the color of the camera blends into the background. You could always disguise the camera but leave the lens area open like I did with our birdhouse cams.
........ it may be easier to hide / disguise the camera itself.
.......it seems to me this is the right direction in my case.