I'm not personally aware of anyone showing an example of using Google Cloud as an externally usable Iceberg REST Catalog, but that doesn't mean it isn't happening with someone. When I look at the Google doc page you supplied, I don't see any mention of them supporting a REST Catalog for engines like Trino & Spark. Even the diagram shows them going directly to the metadata files (bypassing the BigQuery Metastore?) with the comments of "OS engines can query (read-only) using metadata snapshots". Usually, the REST Catalog gives the query engine the name of the current snapshot's metadata file and then off to the races from there.

Even the "view iceberg table metadata snapshot" section talks about manually figuring out the metadata snapshot file instead of getting it from a REST Catalog. Additionally, it looks like the "read iceberg tables with spark" section isn't using a REST Catalog either -- it seems to be pointing to the HadoopCatalog provider which I'm thinking just allows you to hand-jam the metadata file stuff too.

Again, not suggesting this all can't work, but I surely haven't seen anyone do it yet. I'd look for that BQ doc page to show an example of how they imagine Trino would connect to one of their Iceberg tables.

In addition to chasing Google on this, there are slack servers for Trino and for Iceberg where you might get somone else who has attempted this. Sorry I don't have any real suggestions to offer -- just my $0.02's worth. ;)