According to the Odoo manual, Odoo provides support and bug fixing for the last 3 major versions of Odoo. Look here. https://www.odoo.com/documentation/18.0/nl/administration/supported_versions.html
Summer 2024 this meant that:
https://www.odoo.com/documentation/17.0/nl/administration/supported_versions.htmlAnno Summer 2024 means that:
* current version 17 (released in November 2023, available since February 2024),
* version 16
* and version 15
See the screenshot below (For up to date:
click here or above on the link)):
Odoo saas = Odoo online = these versions are not available for Odoo.sh

Odoo SA provides the technical updates in the Odoo online (saas) environments.
dooIT BV provides together with Odoo SA the technical and functional updates in the Odoo.sh environments.
Our advice is therefore even: update at least every 2 years (version difference maximum 2). Why?
* Odoo develops quickly and a lot - take advantage of all those new handy features
* The difference between versions is large - make sure we both still know your version to provide/get optimal support (for migration)