proj_create_from_database: Cannot find proj.db when trying to open a QGIS project in Python

I am trying to write a standalone QGIS script that opens an existing QGIS Project in Python3.
Upon Calling project.read('filename.qgz') (projct being an instance of QgsProject) I get the following errors:

proj_create_from_database: Cannot find proj.db
proj_create_from_wkt: Cannot find proj.db
proj_create_from_database: Cannot find proj.db
proj_identify: Cannot find proj.db

I have set the PROJ_LIB environment variable to the directory proj.db resides in (%qgisPath%shareproj), but that doesn’t change anything.

I’m on Windows 10, running QGIS 3.14, but I had the same problem in QGIS 3.10