I did this. I just had to resign myself to it being an ongoing process.

I did NOT do forwarding. It was the easiest way to identify what's still associated with the old address.

It was not a clean break. I still have the old account, and occasionally it turns out something is still contacting me at it. That's ok... 99.9% free and clear is better than 0%.

Getting people to stop emailing my old address was annoying. But also, there were fewer people than I thought that still email instead of messaging. Email is mostly account stuff.

I decoupled. When selecting a new service I intentionally did NOT look for, or use, ten services at one provider. Provider stickiness was what makes the process painful to begin with.

Some accounts will not let you change addresses, ever. For those I just bit the bullet and deleted old accounts and made new ones (like ecobee).

The IdP thing wasn't a huge deal, but I don't do a ton of that anyway.

I also moved to a better password manager, and that helped keep track of what I had moved.

I did some takeout process stuff. Aside from the opportunity to clean up and reimport contacts, I don't think I ever used most of it. Most things were just less important than I thought they would be.