Humidity tolerance of Mod Podge
It might resist air humidity for a while, but I would opt for a more water resistant variant like &quot;Outdoor Mod Podge&quot; or &quot;Dishwasher Safe Mod Podge&quot;.
The following information is taken from Is Mod Podge Waterproof?

Mod Podge is a craft supply made up of several ingredients, including vinyl acetate. The combination produces a product that is somewhat water resistant, but not waterproof.
If a few drops of water end up on your Mod Podge project you can wipe them away with ease. You aren’t going to ruin your craft with just a little bit of water.
Note: if water is on your Mod Podge project for an extended period of time, you might notice some clouding. Typically when you remove the water the Mod Podge will slowly dry to clear again. However, you might see some permanent cloudiness and/or rings.

As long as your artwork isn't subjected to the water stream from the shower, it should be fine. Usually in a bathroom there are times of high humidity, followed by longer times of dryer air. The normal Mod Podge might get sticky or cloudy over time (I have no experience with that), but more resistant variants should resist mist and humidity long enough until the air is dry again.