I double checked my codebase and it looks like it's just JSONB, which CockroachDB also doesn't support [0]. Sorry to bother about missing features, but there are really some things that prevent a smooth transition from Postgres.
However Odoo leans heavily on Postgres, migration would be a lot of work I imagine. The first snag I've hit with CockroachDB is the lack of 'CREATE SEQUENCE'.
Plus, Odoo uses REPEATABLE READ + a hand-rolled system of locks for consistency, I'm not sure how that would play out with CockroachDB. In my experience some of the performance issues come more from long lived locks in the app than from sheer DB performance.