Yup! PS, we already gave up Ubuntu 18 support ;). We're using c++20 now, which requires Ubuntu20.

Ah okay, so I guess with this change then we give up support for Ubuntu 18. But hey, I imagine we'd rather have it work with CMake 4.0 than Ubuntu ...

Ok so the git log / changelogs actually tell why, it was to solve this issue on Ubuntu 18: #25 (closed)

I'm not entirely sure why we did it for aoflagger, but I think that the pybind11 version of older Ubuntu's (really talking about 2016 or 2018 and e...

While this MR makes sense to me, why was the dependency a submodule before? Did you want to pin a version or force a build from source?