sci-geosciences-3.26.3 (~amd64) fails in compile phase against Python 3.10.5/Sip 6.6.2. The reported error is: AttributeError: 'ScopedName' object has no attribute 'replace' In https://github.com/qgis/QGIS/issues/49214 the issue is solved by patching sip. By updating to upstream dev-python/sip-6.7.2 I could compile qgis-3.26.3. Sip update was flawless, just updated ebuild version (had only to handle the SRC_URI mirroring).
*** This bug has been marked as a duplicate of bug 877835 ***