Defaulting to user installation because normal site-packages is not writeable
WARNING: Skipping /opt/fsl/lib/python3.11/site-packages/nlopt-2.7.1.dist-info due to invalid metadata entry 'name'
Can you confirm that the conda installation and environment are your own personal ones, and not shared (e.g., in a cluster)? It looks like it may be using the FSL installation conda environment.
Indeed, I think the problem was the FSL installation which is on a server. I re-installed FSL in my own environment and it seems it’s working correctly.