Can you? Yes. Proper primer (oil or shellac) followed by sanding and caulking and a couple layers of Enamel topcoat. The oak grain on the plywood will always show through unless you fill it.

The wood is beautiful and perfect for an office, I would leave it.

Can you just change the floor and the window covers to something lighter?

I was thinking the same as @J Steel - and I wondered about the furniture because it looks as dark as the wood. Painting the wood seems so drastic & permanent & for all we know, it goes very well with the rest of your home. The wood color of blinds doesn’t show well in the photos as far as a good complement to the walls. Changing the floor would be a major investment too - just as much as painting the wood. And, again, what about the flooring in adjacent rooms? It would be helpful to see the entire room & adjacent areas. But, based on the small peek at space, I’d change blinds to a same style neutral color, add a light color patterned area rug & update the desk furniture to a lighter color & less bulky style. Or, maybe refinish or paint the desk.

Yes, as @HALLETT & Co. noted, it can be done with the proper prep work and priming.

I love great wood but this is not that. Looks like pine trim, oak panels, and maple cabs all unified with blotchy gel stain. Paint would help this space tremendously.

What about limewashing, like rubbing on a thinned white paint that would let the wood grain show through some? Easier to switch to lighter furnishings and window coverings with a creamy colored rug. Lighting also makes a big difference. I actually like this paneling that hubby won't let me limewash in our living room when we have our lighted Christmas garlands hung.