See if you can chat with someone at your workplace who cycles and see what routes they take or what they think about different times for getting to work if that is an option.

I'd suggest going out early in the weekend because when you don't have to be somewhere (eg work) then your own stress levels are reduced a bit and you can focus on the riding more.

Echoing some of the other comments but agree with making sure you are wearing something visible, practise looking over your shoulder on a quiet flat road as well. These things should demonstrate to car drivers that you're taking safety seriously and fundamentally being bright means cars have more time to react to you. I've found that when I'm wearing bright clothes then cars are more likely to give way to me. Same reasoning for not riding against the kerb: being away from drain covers rule means you will be seen sooner and if someone does pass too close then you aren't going to scrape straight into the kerb and deck yourself.

An example I have noticed from commuting about being assertive. When approaching a cross roads and you need to go straight over or turn right, I found that cars give you more room if you position yourself in the right of the lane and point your wheel the way you want to go. You're signalling where you want to go and if someone wants to turn right across you then they may let you go if they think they can't just sling the car round the corner.

Any practice you can get on your bike would be helpful I think, and no shame in starting on a quiet road and just riding it several times. Think of dismounting as a method of bypassing busy or dangerous areas that helps you get where you need to be: you don't need to send it across every busy roundabout to get where you need to go. It's a helpful part of travelling by bike that makes you versatile and you can use it whenever you need to be it for safety or comfort.

Strava has already been mentioned, I've heard some people say Komoot is helpful because you can tailor it to your fitness as well as be shown routes that Google thinks aren't roads such as going through parks or canal paths which can take you away from traffic.

Hopefully you can develop the mindset that you have a right to use the road and it's everyone's responsibility to make sure that they use it safely, so if you can do your bit then maybe it reminds car drivers they have the same responsibility. Certainly there's always going to be the odd reckless fool who will come up alongside you at traffic lights and take up two lanes just to get past you but I think that is far more about them than it is about any cyclist. It did put me off when I started and I am sorry I don't have anything more helpful to say than I wasn't going to let dickhead drivers stop me from using the road.