Think about what he actually spends time doing or thinking about.
If he games get the latest game or gaming headset. If he works out get gym gear or protein powder. Tech lover would appreciate wireless earbuds or smart watch. Outdoorsy guy needs camping gear or hiking backpack. Foodie boyfriend would love cooking gadgets or gourmet food collection.
Sports fan needs team merchandise or match tickets. Luxury watch if he appreciates nice things. Leather jacket if that is his style. Power tools or DIY equipment if he fixes things.
Subscription box matching his hobby like coffee, snacks or books. Experience gifts like adventure activities or concert tickets beat physical gifts usually.
The worst gift is something generic that could be for anyone. Best gifts show you really know him and his interests. Add a genuine birthday letter and you have a winning combination. Thoughtfulness and personalization matter infinitely more than price tag.