What type of wood do you give him? Different types of woods have different flavors so you might just not have found the right type of rabbit safe wood that they like

Have you tried fresher woods? I.e newly picked branches and twigs? Willow sticks and leaves are a massive hit with my two, the fresher the better 😊 they will sometimes ignore old dried willow but go crazy for fresher sticks.

Apple twigs are the favorite here. I ask people that prune there trees in the winter if I can have the twigs (they just go to composting otherwise). (Important that the trees arent treated with pesticides though).

Ive never tried to flavor wood. Boil pieces in apple juice perhaps? Seems a bit wasteful though.

My bun likes to gnaw on her IKEA bed, and on my bed, which also is fir.

If your concern stems from dental health, as long as they are eating a healthy amount of hay, you do not need to worry about a lack of wood chewing!

That being said, Oxbow released a guide on coloring wood, so maybe that can serve as a nice basis for flavoring methods: https://www.oxbowanimalhealth.com/blog/make-your-own-diy-pet-safe-dyes/

My bunnies chew everything. I’ve had to put wire mesh over things so they don’t chew on the stuff there not supposed to and even then they find other things to chew like the front door, furniture, couch, despite having lots of hay and willow branches and logs to chew, plus chew treats but they prefer the painted door frames and corners of furniture and literally anything. They are slowly learning what they can, and can not chew with some experimental training techniques. I wish there were a spray I could get that rabbits don’t like the taste off but safe. In the states you get get things like Sour Apple spray but I can’t find anything here in the UK. They are slowly learning either way so its all good.