That is commonly done, and yes, any pyrex is fine for it although metal has an advantage in that it wouldn't require extra time.
Anytime you use glass, pyrex, ceramic or any other heat absorbent material for "pot in pot" cooking, add ~5 minutes to the time under pressure.
Anything that is safe to use in the oven is safe to use in the Instant Pot.
Whatever you use inside the liner of the Instant Pot as your cooking vessel, use the trivet and add water (at least 1 1/2 cups or so) to the inner pot of the Instant Pot, and be sure there is some room (it doesn't need to be much) to allow steam to pass between your inner pot and the Instant Pot liner.
Here's more on the subject of 'pot in pot' cooking.
cooking.stackexchange.com/users/20183/Jolenealaska
I am new to Instant Pot also.
Had a "chat" with Ranier at Instant Pot today to ask about glass dish to use in Instant Pot.
Was told that anything that is oven proof is okay or to use a smaller Instant Pot insert.
Mine is a six quart.
I was ready to throw it out the back door last week because I was having such a hard time putting lid on.
This is going to be my favorite fun kitchen gadget.
cooking.stackexchange.com/users/63470/2017COOKERgirl
If you want to have a minimalist kitchen, a good option is oven-safe Glasslock, which has the advantage of also providing a convenient way to pack food for refrigeration and transport.
It's also available in a variety of stackable sizes; obviously round Glasslock will fit more efficiently in an Instant Pot than will square or rectangular.
cooking.stackexchange.com/users/3627/intuited
Manufacturers of Pyrex, Corningware, and Anchor Hocking do not recommend their products in the Instant Pot.
I emailed, chat with them.
cooking.stackexchange.com/users/75539/June
I am making chocolate pots de creme and also at times I like to make creme brulee
so I use individual ramekins in the Instant Pot to pressure cook.
cooking.stackexchange.com/users/65522/Kim L.
What pyrex would be suitable for pressure steaming in an Instant Pot (also known as 'Pot in Pot' cooking)?  I am a new user and want to make sure I have the correct cookware.
Pyrex that can be used in an instant pot
cooking.stackexchange.com
<equipment>
cooking.stackexchange.com/questions/80862
cooking.stackexchange.com/users/57062/Debbie H
While manufacturers of Pyrex, Corningware, and Anchor Hocking do not recommend their products in the Instant Pot, anything that can be used in the oven should be fine. A metal bowl would take less time to warm up though, and other options would include oven-safe Glasslock or individual ramekins. Pyrex may or may not be safe in the Instant Pot. However, other oven-safe dishes, Glasslock and ramekins can all be used safely.
It is debatable whether pyrex can be used in Instant Pot. The manufacturers do not recommend it. Products that are safe to use in the Instant Pot include oven-safe dishes, Glasslock and ramekins.