FindPython doesn't support backporting any more in 3.25
The FindPython module was originally designed to support backporting to older CMake's (3.7 initially). I used this fact when designing scikit-build-core; it provides a backport of FindPython and supports CMake 3.15+. This is tested and works for 3.24. However, in 3.25.0, it's now broken; it cannot be used on older CMakes anymore. This is important for us to provide the fixes and features for Python users that go in during the project lifespan, including !7917 (merged) and hopefully #24141 (closed).
This is what is broken:
Policy "CMP0134" is not known to this version of CMake.