It should all be opt in

Then you introduce self-selection bias and the data is worthless.

Aggregate data can be used to personally identify

You can’t identify someone based on how they interact with a service. If you spend 5 minutes on one page and 2 minutes on another that could be anyone. Even if you for some reason personally knew someone’s browsing habits it would be nearly impossible to pick them out in a sea of millions of data points.

I see you linked privacyguides.org in the thread as “alternatives”, one of the services it recommends is Proton (Mail, Drive, etc.). Look at their privacy policy:

2.1 Visiting proton.me or protonvpn.com website: We employ a local installation of self-developed analytics tools. Analytics are anonymized whenever possible and stored locally (and not on the cloud). IP addresses are not retained and stored for such analytics.

When you use our native applications, we (or the mobile app platform providers) may collect certain information. We may use mobile analytics software (e.g. fabric.io) app statistics and crash reporting, Play Store app statistics, App Store app statistics, or self-hosted Sentry crash reporting to send crash information to our developers in order to rapidly fix bugs.

Or how about addy.io that privacyguides recommends for email forwarding? From their privacy policy:

We use a self-hosted instance of Umami, an open-source, privacy-focused and lightweight option for website analytics. All the site measurement is carried out absolutely anonymously.

ALL online services collect this kind of data. Even the privacy-focused ones. There is nothing nefarious about it.