Turn on the Finder extension
M-Client switches on its Finder extension at every launch. If someone turned it off, M-Client Settings shows an orange Turn On… bar.
To turn it on yourself, open System Settings ▸ General ▸ Login Items & Extensions, go to File Providers and turn on M-Client Finder.
The exact wording of System Settings differs between macOS versions. Search System Settings for "Extensions" if you cannot find the entry.