How to avoid excessive steam build up in oven

What settings does your oven offer? Usually an oven should have proper venting of excessive moisture. Are you maybe using a special "steaming" setting instead of regular heating? If it's a regular setting that you're using, your oven might have a technical problem with ventilation that a service mechanic might be able to fix.

As a meantime band-aid fix, you might want to quickly open your oven door ever so often to let out excessive steam. If this does nothing to reduce the amount of steam, it might indeed be a steaming setting that somehow traps or even injects moisture into your oven chamber.

You can use the fan setting and have a very small opening at the door so you force the steam to escape. Please note that depending the recipe we want to have moisture inside (chicken). So not having any moisture as cooking can cause your chicken to be extremely dry. Best way is just to open the grill with fan for a 15min at the end of cooking.

Your problem isn't humidity. It's water, and temperature.

A closed oven which has a significant amount of food in it will be quite humid, in the sense that the gas inside it contains a high percentage of gaseous water (aka steam). It's possible for food to crisp up, and even burn, even with that steam being present.

But that high percentage doesn't equate to much mass of water. When the oven is hot, the density of the gas is low.

Assuming you preheated the oven, it was hot. But when you open the door and see a big cloud of vapor, that means that the oven had cooled off, probably because of evaporative cooling (as water evaporates off the food, it cools both the food and the air). It's the cold oven that's limiting your crisping.

If there's a lot of water, and a lot of surface area for it to evaporate off of, and not enough oven power to build up a temperature gradient, the food can effectively hold its own temperature down. This is what causes "the stall" when BBQing, and it's what causes limp, moist oven fries.

Potential solutions:

1. Increase heat flow to the food by using convection if available, or by using all heating elements if your oven has multiple independent elements.
2. Decrease evaporative cooling by cooking less food at once.
3. Cook longer. Once you've dried out the surface of your food, evaporative cooling stops, temperature rises, and crisping/browning picks up.
4. If you weren't preheating your oven, preheat your oven. The oven walls have a high heat capacity which buffers the evaporative cooling.

Things that are not potential solutions:

1. Opening the oven door. I know it seems like that's "letting the steam out", but the steam was going to come out anyway; you're just letting the heat out with it and slowing things down.
2. Increasing the temperature. This doesn't make your oven work harder! When it's being limited by evaporative cooling it's already working as hard as it can. Redlining the thermostat is just going to put your food at risk of burning.