I will just say, this isn’t just a “you” problem, but a “team” problem. I’m loud and opinionated in meetings. And frankly a good manager or senior dev should be thinking of directly soliciting thoughts from quieter members of the team (and shutting up the loud ones a bit). It’s on them to create an environment that feels safe for you to voice your thoughts and it’s also on them to give you encouragement.

Of course it’s on you to have something to say. I think “I don’t know, let me think about it and get back to you” is probably one of the wisest things you could say. Quiet people, slow to opinion, can contribute a great deal this way.

It also wouldn’t hurt to force yourself to do some public speaking. For example a friendly meetup or an internal team lunch and learn. These groups are most of the time very welcoming and grateful for any talks they can get. This will help build your confidence in group settings. Who knows, you might even grow to enjoy it?