And now we planned to stain them, but getting a cold food in doing so (expensive cost, life destruction, they look nice without stain, laziness etc - some of the reasons).
I went to the site, it was very slow to open.
It looks like the window frames are fiberglass on the exterior surfaces and the interior has some sort of wood veneer over the fiberglass? Okay--is it bare wood right now, or is it finished in any way? If it is bare wood, you really have no choice but to put a finish on it, and do it soon. Whether you stain the wood or not, it needs a protective coating to keep moisture, dirt, oil from hands that touch the frames, etc from penetrating the open pores of the wood veneer. Once this happens, the normal fix is to sand down the wood to get to new wood and do what should have been done originally--finish it. But veneer isn't thick enough to take much sanding, and the sanding is a lot more work than just finishing it in the first place.
You can't leave the wood bare, it will look dirty in short order and the veneer will likely start to split or detach due to the rapid changes in moisture content windowframes experience, particularly in the winter.
I'd recommend you get some wood samples of similar species and "cut" to the veneer you have. You can even get some veneer. Then, try some stain samples (you can get little packets of Varathane stains inexpensively), and then try some different types of durable top finishes. You'll probably want to use a polyurethane top coat--likely 2-3 applications. And you might try the top coatings without any stain, too--it will likely be a little darker than the bare wood you have now, but it won't artificially enhance or diminish the grain patterns as much as some stains do.
