How do I opt out of contact tracing?

As it is not enabled by default, and you would need to download a very specific app, there is nothing to opt out from.

You just don't download an app using it, and don't opt in when that app asks for premission.

It's opt in, not opt out.

How do I opt out of contact tracing?

You can't opt out of something you have yet to opt in to.

It is off by default so you do not have to opt out. Plus, you would need to download an app before you could even start to use it.