A recent (Feb’25) post on the Sonos forum suggests that Innuos still use the old insecure v1 of the samba/SMB protocol, so in terms of a simple network share (I.e showing under “Shared Folder” under Home Music Share in the WiiM Home app - if that’s what you mean by the pro plus “seeing” the Zen), it’s not compatible with WiiM devices which use the more up to date secure SMB2/3 protocol.
However, if you have indeed enabled the Zen as a UPNP server in the innuos app settings, then it should appear as a “Media Server” under Home Music Share and allow the WiiM Home app to browse and play files stored on the Zen.
Where the Zen appears or doesn’t appear in the WiiM Home app (I.e. either Shared Folder or Media Server) would confirm which route you are perhaps trying to take, hence my request for screenshots.
If you’re using neither Squeezer or the WiiM Home app, please elucidate.