Your issue is not with the plugin, your issue is with mautic installation.
NPM is required for Mautic 5 since its building some JS dependencies via that - this was not the best idea in my opinion.
You are not the only one who faced the issue either:
< Composer Setup for Mautic 5 Now Needs NPM >.
The simplest solution is to install npn and then it will run the build as finish the installation sequence.
The thing is that the build process should not be done on the production server in the first place.
The proper way to do this is to separate / isolate the generation of JS assets and then after they are built, they get transferred to the server.