Dealing with high temperature and low humidity in small greenhouse

I have a 2x2 meters polycarbonate greenhouse and I’m struggling to keep temperatures in the 23-28 °C range during the day in direct sunlight. Between 12 pm and 3 pm it can get as hot as 35° C even with door, side vent and roof vent open. Naturally, that interferes with the humidity level that drops to 20-30%. I’ve found that opening the greenhouse does reduce the temperature a bit but it also lets the humidity out (I’ve a 4 L humidifier but does nothing in the day, as the humidity is blown away by the air. It does work in the morning and night when I can close the openings). Even with morning waterings to the floor (dirt and grass) and pots do almost nothing in those hot hours.
I place a shade cloth that works to some degree, keeping the temperature below 30 °C, but it loses some of the sun rays that my plants need. Also, that doesn’t fix the issue with humidity. Everywhere I read it says that ventilation is key in order to keep the temperature down but that way the humidity just can’t keep up as it escapes the greenhouse.
What can I do? I’ve think of foggers, industrial humidifiers and more solution relying on increasing the humidity so the temperature drops but the greenhouse is so small and crammed that it seems difficult to implement those ideas. Besides, there are fans, lights and a heater inside that can get wet. I plan to upgrade to a bigger greenhouse in a few months but everyday I have to deal with this issue until then. Please help! My plants aren’t very happy.

Look into whitewashing options. It is reflective rather than just shading. I normally recommend woven aluminum and personally use Aluminet but you might want to wait until you have the larger greenhouse to make the investment. Mine just went up and will stay on until September.

I have had misting systems attached to the roof supports with large binder clips and on timers. It doesn't sound like your electrical is waterproof. Besides, adding a lot of humidity without proper air circulation and ventilation is a recipe for disaster. I know this challenge because my greenhouse is maintained at 60% or higher.

As for humidity control and temperature you will ultimately need an evaporative cooler, aka a swamp cooler, in your arid environment. That should solve both issues. Unfortunately a small greenhouse requires the same conditions, ergo the same equipment, unless you can find creative alternatives.