Chromium is open source. And unsurprisingly all the data collection bits are open source too. (They call it UMA metrics in the codebase.) Search in the codebase for things like UMA_HISTOGRAM_ENUMERATION or SCOPED_UMA_HISTOGRAM_TIMER and with a free afternoon you'll have a pretty good idea what kind of telemetry Google really collects.
Chrome is closed-source though. There’s no way to make a reproducible build of Chrome (the Google binary adds DRM and could be adding more).
I’m mentioning this, because this open-closed ambiguity is a typical Google strategy. Similarly, Android in the AOSP flavor is open, but the OS that actually ships on phones is different.
Example: https://source.chromium.org/chromium/chromium/src/+/main:bas...