In QGIS, I can create a custom user projections. Create a layer that uses that projection. Save that to a geopackage (gpkg). Then share that gpkg. The layer can be viewed in another instance of qgis, however the user projection does not auto import. By import I mean being able to see the custom projection in their master list of projections.
I am aware that a user can manually create a custom projection given the projection information via a WKT projection description or proj4 string. I would like to avoid this.
From the related question a comment suggests importing a layer with arbitrary projection and selecting "Set Project CRS from layer" This will be the fall back at this time, but hoping to learn an import option.
Ideally I would want something like "set this flag", so that another qgis instance will just auto import the projection.
How do I save a layer to a gpkg with user projections that will trigger auto import of user projection? Are there values that I can change on the creation end, preferably via pyqgis?
Import projection from existing layer This question is different in that I am trying to find out if there is something to be done on the creation side, whereas the related question is all on the import side. Additionally, gpkg at the time of that question was not big, there might be something specific to that.