Optimistic Locking functionality in an RMB module is enabled for selected tables by changing configuration in the schema.json file. See https://github.com/folio-org/raml-module-builder#optimistic-locking. OL changes the behavior of the API and hence requires a major interface change.
It has been discussed that OL 'failOnConflict' should be enabled for interfaces where there is a risk of concurrent access (and collisions). In mod-inventory storage this is done for instances/holdings/items.
POs: indicate interfaces where OL should be enabled by creating a specific backend issue and linking to this feature.