Project mode is a beta feature of the beta R-releases introduced in v17R5 beta.
To use project mode, the database must also be compatible to enable Object Notation.
If an older database is converted to v17Rx and is not compatible to enable Object Notation or use Project Mode, converting the structure to a project will geneate a log in .json format revealing all of the issues that prevented the structure from being properly converted.

Addressing the items in the log will not only allow the database to beconverted to a project, but it will also allow object notation to be enabled.