Analytics are not theme related, and not covered by theme support. We tried to look at some basic support and tutorials, but the scope is just too broad and far too specialized for us to offer any real support or guidance for.
99% of users will find that the Google Site Kit Plugin does what is necessary. For anyone requiring further assistance, we recommend https://www.nerdpress.net/
Google Site kit
Our recommendation is to use the Google Site Kit Plugin, which is developed by Google to support their own analytics product. As of July 2023, all users have been forced over to GA4.
Trellis Analytics
The Trellis Analytics feature will output the Trellis analytics tracking code for users that have migrated from Trellis:
We recommend replacing this with the Google Site Kit plugin.
The Trellis Analytics output will automatically disable itself if it detects the Google Site Kit plugin is installed and active.
Other analytics
Grayson from imarkinteractive has suggested Clicky or Plausible as an addition for real-time analytics that GA4 lacks.
Mike Zielonka recommends Fathom Analytics.
Microsoft Clarity is also a potential replacement, but may have INP (a core web vital for pagespeed) issues.
Experts
If you'd like additional help setting up Analytics, we've heard good things about: