Student or Learner
Which sentences are correct?
I don't agree with his suggestion.
I don't agree to his suggestion.
I don't agree with his opinion.
I don't agree to his opinion.
1 and 3 are uncontentious.
You can use 2. in the sense of "I don't agree that we should do what he suggests."
It less likely that you will find a use for "I don't agree that we should do what he opines."
A suggestion is a more concrete utterance than an opinion. A suggestion usually calls for action, but an opinion doesn't necessarily.