Dude you’re only 6 months into your current position, I think you’re being too hard on yourself. It’s normal to feel incompetent; your industry is new to you and you’re still relatively fresh out of school. I think what’s setting in is how little you actually know about your industry or role and this is normal. What’s important is how you set yourself up to dig yourself out of that knowledge/experience deficit.

It’s good that you’re asking lots of questions, sucks that your SMEs aren’t that welcoming but this might be an opportunity to learn how to adjust your approach when dealing with difficult people. You didn’t mention how often you ask questions or how you structure your questions but when working with folks that aren’t too receptive, I’ve found it’s best to compile lists of questions to ask in a single session as opposed to pinging throughout the day. I’ve also found it’s best to lead discussions with recapping what I’ve done to find the answer myself.

Regarding your manager approaching you about expectations; I’ve got two potential hot takes.

1) no one hires an entry level engineer expecting a lead or SME level of experience. If your manager doesn’t talk to you about your expectations then it might still be good for you to ask about expectations and ask often so you know what you need to be working towards.

2) getting feedback, even if negative, this isn’t exactly the worst thing to hear when your at this stage of your career assuming a) your job actually cares about your development and b) you take that feedback constructively and fix it asap. Again you’re still discovering what you don’t know from a technical and possibly interpersonal perspective. You want to know what are areas you need to focus on while it’s okay for you to make mistakes as opposed to carrying bad habits to future positions, where those habits might be unacceptable from a mid-level engineer.