For bulk operations (insert, update), Retool fails to call the BigQuery API with the proper flag to enable session management i.e. BEGIN, COMMIT and ROLLBACK have no effect. BigQuery even logs an error for these statements: Transaction control statements are supported only in scripts or sessions.
Effect: minor as Retool sends one insert with multi-values so if one values-insert fails, the statement fails (and I assume no previous inserts are saved).
Fix is simple though: Retool should either not use session keywords, or - better - pass the correct createSession flag: Criar sessões | BigQuery | Google Cloud