Just stumbled over ungoogled-chromium and for me it sounds like this should be the variant installed from the PureOS repositories.
1. Remove all remaining background requests to any web services while building and running the browser
2. Remove all code specific to Google web services
3. Remove all uses of pre-made binaries from the source code, and replace them with user-provided alternatives when possible.
4. Disable features that inhibit control and transparency, and add or modify features that promote them (these changes will almost always require manual activation or enabling).
Sounds for me like exactly what Purism stands for.
Furthermore the thought came up that this might be necessary to keep the FSF endorsement, if “Remove all uses of pre-made binaries from the source code” is meaning what I understand: “Remove parts that are not contained as source code, but as ready made binary blobs”.
I didn’t look into chromiums source to verify that this translation fits and would be thankful for any insight.