Hola Mayan!
The goal in general when reducing ecological impacts from home products is finding ones that are:
-Created from biological sources and organic materials
-Zero to minimal toxic substances or chemicals, like heavy metals, VOCs (Volatile Organic Compounds), plastics, etc
-Not made from fossil fuel products
-Locally sourced
-Ethically created
Some good options that match these criteria, that are good for wood preservation are Linseed Oil, and Tung Oil (though Tung is imported so can’t get a ‘perfect score’).
Here is an article and video discussing how to apply Tung il to preserve wood. I assume it’s the same process for Linseed Oil.
https://mountainmodernlife.com/natural-wood-sealer/
Another product I’ve heard can work well in areas not getting direct sun is Bee’s wax. Here’s a resource on how to apply that to wood.
https://startwoodworkingnow.com/how-to-apply-beeswax-to-wood/
Have fun!