Tilt the lid.
It will stay where you put it… approximately.
See pan top left & pyrex bottom right
; they will stay like that all day if needed If it really refuses to stay, then wedge a spatula [or any other bit of wood or plastic (& of course, not metal if it's going in the microwave) of any appropriate size]* in it, either from the edge, down the handle, as at bottom left, or right the way across then balance the lid on top of that, as at top right.
The latter will also go in a microwave.
*
This is physics 101 - put something in that
's big enough to hold the lid ajar, yet not big enough to get in the way of anything else & not small enough to fall in & get lost in whatever you're cooking…
cooking.stackexchange.com/users/42066/Tetsujin
Funny enough, I saw a little silicone gadget the other day when I was out shopping - those stick men called Lid
Sid are designed to do exactly what you want.
Granted, they are real unitaskers, but also kind of fun.
Other manufacturers make similar items in other shapes - I have seen sheep, witches and others.
cooking.stackexchange.com/users/28879/Stephie
A different option is to use a silicon lid.
You don't have to leave it open, you just cover the pot fully and it bleeds off steam on its own just like a tilted solid lid.
cooking.stackexchange.com/users/4638/rumtscho
I have a rice cooker where the lid's vent hole is slightly too small, so I've done this by propping the lid open with a chopstick on one end of the lid.
If you want it to be evenly vented, you could put one chopstick on both sides of the lid.
cooking.stackexchange.com/users/22743/Milo P
If you were doing this a lot it might be worth making a little thing with an H shaped cross section (like a bit of a girder), one pair of legs straddle the rim of the pan and the lid rests on the others.
You could make it asymmetric to get variable heights.
You'd have to consider the material carefully, i.e. no metal if it's to go in a microwave, some woods & plastics are more heat resistant than others.
cooking.stackexchange.com/users/76953/Bloke Down The Pub
Probably we could use plastic cloth clips clipping them on the walls of a bowl, cover would stay atop of them.
Probably it's ok, though there's metal spring which can cause problems.
cooking.stackexchange.com/users/40922/R S
If you need to keep cover of pan or bowl slightly opened during cooking, what's the best way to do this. May be there is devices for that, if so preferably non-metal. Specifically glass bowl like Pyrex in a microwave.
What's the best way to keep cover of a pan slightly opened?
cooking.stackexchange.com
<boiling><pan><moisture>
cooking.stackexchange.com/questions/103905
cooking.stackexchange.com/users/40922/R S
You can tilt the lid, use a silicone lid or prop the lid up with a chopstick or another object. Tilting the pan lid is the easiest way to keep it slightly open However, there are gadgets specifically made for this task. Moreover, many gadgets for this task can be made at home, using easily available household items such as chopsticks and pegs.
Tilt the lid or use a silicon lid. Buy a gadget made specifically for holding the pan lid open. Make your own gadget for holding the pan lid open, using chopsticks or other itams found at home.