Seems that FermiTools 2.4.0 require very specific python version for the installation:
fermitools 2.4.0 would require
│ └─ python >=3.11,<3.12.0a0

For me the installation worked only with python version explicitly specified:
conda create --name fermi python=3.11
source activate fermi
conda install -c fermi -c conda-forge fermitools

With the default installation instructions on wiki:
conda create -n fermi -c conda-forge -c fermi fermitools

conda (25.3.1) was not able to solve environment, freezing at solve environment step.