Parsing the meaning of opinion and distinguishing opinions from judgments from facts from truths from matters of taste is a deep philosophical well that I doubt any of us are equipped to properly dive into.
For example, if the one and only acceptable definition of opinion is a belief or judgment that rests on grounds insufficient to produce complete certainty, and I say, "raw onions are disgusting," that isn't an opinion. I've eaten raw onions and I have grounds sufficient to be completely certain that they are disgusting. You may think the exact opposite and neither of us are wrong and neither of us are expressing an opinion.
Another example: Mike Trout is a better offensive player than Alcides Escobar. That isn't an opinion either. I have sufficient grounds to say that with certainty.
But, I'm not a car mechanic. If my car is acting up and I say, "I think it needs new spark plugs," that is an opinion. I do not have sufficient grounds to produce complete certainty that the plugs are the problem. And it's an opinion that could be wrong.