I may have a unique perspective on this;
In hindsight, when I was younger (late 20s) and put in charge of a small team, I had an employee under me in their early 50s quit, and give an exit interview very similar to what you've written.
Apparently I "didn't recognise his contributions" or "value his opinion", or "use him to his best ability". I "gave him busy work". He was the oldest team member by about a decade. I was the youngest manager, I was technically still at uni when made manager.
His departure took me by surprise; I thought I did value him, I thought I did value his contributions. Shortly after I left that company and got a new job as a developer. Haven't managed people since.
- He had an accent I struggled with, and a good chat was a lot of effort. I found him difficult to small-talk with, and after 12 months I couldn't tell you anything about his interests, family, or who he was outside of work.
- I also was uncomfortable with the power dynamic. He's old enough to be my Father, yet I'm supposed to be developing him.
- The combination of accent and power dynamic made me want to reduce interactions - I'd give him work which could be assigned in bulk, and was obvious when it was completed. So that I didn't have to micromanage, and didn't have to review what was done at the end of it.
- This resulted in a segmentation of my team - he was working on one thing, everyone else was working together on a more complex task. The complex task needed a lot of discussion and brainstorming, and he was present at these, but because he wasn't working on it he did get skipped while asking people their thoughts more than once. I thought nothing of it.
- When crunch hit, I kept him working on his regular area because I needed that maintained and stable, it was the rest of the team who did the long hours of unpaid overtime to meet the unrealistic company demands. I (probably incorrectly stereotypically) valued his time more, assumed he'd need to be home with his family while my younger 20's guys worked late. I never took steps to confirm or deny this stereotype.
My advice to you, OP, is don't assume your manager has it in for you. I didn't have it in for this employee, yet the screw up is on me and me alone. Your manager is probably failing upwards (like I was) and doesn't realise his mistakes:
- Ask your boss directly for something different. "I could do with a change after so much maintaining X - do you need any help on Y? You know I helped write that right?"
- He may be cutting your off because he's in a hurry, he may be cutting your off because of zoom lag, he may be cutting your off because he's impulsive and already moved onto the next problem, (or he may be dismissive of you). A polite "hang on I've got more" after he cuts you off should help you clarify which one.
- Also "okay", "yes sir" or "understood" all sound like something said by someone trying to actively listen and acknowledge you. Now there could be tone or non verbal communication not encoded in text here, but if he pauses after saying that he isn't interrupting you, he's trying to acknowledge he's paying attention, ironically to encourage you to speak. This is really only interruption if he cuts your off and goes: "Understood, and Sally what do you think?".
- "Yes sir" is an honorific, unless he says it cackling with obvious sarcasm I think it's pretty obvious he respects you a lot. I would not expect to hear this from boss to employee in any culture.
If the above can't address it subtly with your boss, try to talk with your coworkers about it to confirm you are reading the situation correctly.
Then, confront boss, in private. Don't assume he's doing it intentionally, leave the HR complain stuff until you're absolutely certain.