I had this problem with my dog when I adopted him too. His front claws grow crazy fast and we don't do much pavement walking with him to grind them down.
If his claws are really bad, as in causing him pain, starting to curl over, etc., then sedation would be the best option IMO, if it's possible.
But longer term, you can genuinely fix the problem through desensitisation. It takes time. Maybe a few days, or weeks, or it can take months. Depends on your doggo. But it will make all the difference and will mean that groomers can do it in future, or you can do it yourself.
This is what we did with our dog, and I was convinced it would never work. But now he's fine with having his nails trimmed. I'd say it took about 6 months to really get it sorted, and now we trim them once or twice a month. One of us feeds bits of cheese/sausage, while the other clips the claws.
All you need to do is start slowly. Get him into a weekly or even nightly 5min routine of being stroked, brushed, fussed, etc. Treat him and softly praise him - make it a really chill, relaxed experience. Don't even go near his paws for the first few sessions.
Then once he's good with that, just once in a while gently touch the top of his paw as you're grooming and petting him, and give him a treat. Over time, you'll be able to hold his paw, then examine his claws, then show him the clippers, then eventually snip a bit of one claw, then eventually multiple claws. Just take it slowly, keep it calm and positive, and you'll get there.
There are lots of videos on YouTube you could watch for the process. This one is really great: