Odoo 18.3 is a release only for Odoo Online.

We have no release of Odoo for On-Premise installation with the AI App and installing Odoo 18.3 On Premise is not supported by Odoo 

Odoo 19.0 will be released later this month for On-Premise Users and this will be the only release we support for On-Premise installations.

See https://www.odoo.com/documentation/master/administration/supported_versions.html