Maybe get him something that he uses a lot. Something practical.
For camping? Get him a custom knife. Extra points if you can him a historical replica knife.
For gazing? Get him a telescope.
Fishing? I'm sure he won't say no to a rod or a tackle box.
Gardening? Gloves, shovel. Hell if there are simply some flowers that you'd like to see out in the garden, buy him some of those. I guarantee they'd be the most treasured flowers in his garden.
Or perhaps you could find something you both have in common. A shared interest. And then go and do that together.
Both of you go to a cooking class or something.
Then there's the option of disregarding what he wants and just doing what you want. It sounds really bad but if the two of you are really close then it might work. My girlfriend does this a lot. Because I'm usually good at getting what I want for my hobbies, she never knows what to get me. So instead she takes me to do something she wants to do.
She'll find a new hobby, I'll get to enjoy watching her have fun and maybe in trying something new I'll like it too and we will have something else in common.
My last birthday she took me to an escape room. She'd always wanted to go but I wasn't too keen. In the end we both loved it, it was really clever. So things like that can work out. But I guess it depends on how well you know your boyfriend, whether he won't be upset with that or not. I'm usually not bothered about birthdays anyway so my girlfriend knows she can risk ruining my birthday and she can make it up to me later if that happens.
Yeah, finally the romantic option is always open. Do something incredibly romantic.
Believe it or not guys like this stuff too. Go to an observatory. Bring loads of pillows to the park with you at night and watch the stars. Wine and dine him. Fire displays. You get the idea, sweep him off his feet.
There are sooo many options. Don't worry about it being perfect or wanting to do everything, you're going to have so many birthday presents to give him in the future so you have the time to get through everything.