I'm trying to query in BQ the custom channel grouping that my company already defined in GA4. Any tips on how to achieve that? I found a lot of posts on creating custom channels inside BQ but not how to query them from GA4 if they have already been created previously.
In GA4 I can use the custom channels properly so there is no issue with the settings. However I'm not sure where is it in BQ. It's not part of the list of events apparently.
Channel Groups are rule_based definitions of traffic sources , Default and Custom Channel groups are not built-in in Big query reports but you can make them by filtering traffic_source.source and traffic_source.medium column values. to know the rules and use them for writing your query check this google guideline or check channel group section in the GA4 admin tab.