There’s an issue tracking TimescaleDB JSONB compression: https://github.com/timescale/timescaledb/issues/2978

Ha, we (my partner at our company) filed this issue 5 years ago. We have a large-ish (but not giant) json blob in one of our timescale tables that I'd love to get better compression on. It changes just frequently enough that we didn't split it into columns, but infrequently enough that it could (I think) be compressed quite nicely. Generally timescale has been great for us.