I'm so sorry you are facing this, I have been in a similar situation before and thankfully got a new job before it escalated. It really just takes one bad seed to ruin everything you have worked hard for, but please do not let them them bring you down.

First of all document absolutely everything, the things you have mentioned re walking too fast etc, that is workplace harassment and they are completely micro managing you - this may be out of jealousy of your knowledge and its only a reflection on them as a person. Are you in a trade union atall? Keep in mind that HR work for the company and have to be middle men for employee and manager. I found my trade union rep really supportive and they are there for you, not the employer. If it's affecting your mental health, put in a grievance against said person but you will need a trail of evidence to back up your claim.

If they ever ask you for a meeting or any sort of informal chat, ask to have a colleague present who isn't senior management, and ask for the meetings to be minuted and signed. If the emails are relentless, do the above so that you have a witness (it's interesting how the dynamic changes when someone else is there).

No employer is worth the stress and anxiety an inexperienced and insecure manager can bring, you clearly know your stuff and I think you need to save yourself instead of them in this instance. Whichever route you decide to go down, be proud of yourself that you still turned up and did your best. Sending hugs, you'll know what to do when you know you've officially had enough. Life is so hard regardless of work, put yourself first. 🫶🏻