What's the correct way to uninstall a plugin which MUST NOT be enabled?
You will need to enable it to uninstall it but you can do everything via CLI.
First ./craft plugin/enable plugin-handle then ./craft plugin/uninstall plugin-handle then composer remove namespace/package-name.
If you really can't enable it as above, you'd need to composer remove namespace/package-name and manually remove any references in your plugins table, project config as well as any tables the plugin may have created on install.