Please bump sci-libs/proj to 6.3.1, which was released 2020-02-11 . sci-geosciences/qgis-9999 (at least) depends on this. Reproducible: Always Current sci-libs/proj version is 6.3.0, which is incompatible with latest qgis-9999.
I guess this is obsolete after 7.0.0 got into tree.