How do I disable a plugin enforced by my host (in mu-plugins)?

You disable mu-plugins by removing the plugin file from the mu-plugins directory. They are outside the normal plugin activation/deactivation cycle “and cannot be disabled except by removing the plugin file from the must-use directory, which is found in wp-content/mu-plugins by default.” I assume you don’t have the authority to remove the files.

The plugins may be using hooks and you may be able to remove some actions or filters and disable all or part of the plugins functionality, but without knowing how the mu-plugins work it is impossible to say how.

But… I suspect your host would shut down your site if you succeed in circumventing something they require. I imagine that requirement to be somewhere in your Terms of Service and not really a surprise to you. If you don’t like the requirement, get another host.