Sharing files from Mac

I have OSMC on a Raspberry and my shared videos are on a HD of my macMini (El Capitan). That works well for years.
I now want to connect a MacBookPro with High Sierra to OSMC. It has the same settings in the Shares tab, but I cannot get a connection.
I first tried from the OSMC via TV. I can enter the IP and a name for the mbp, but it says:
Couldn’t retrieve directory information…
I then opend the OSMC from my other macbokpro in terminal. I can ping and ssh the mini and the mbp from within OSMC.
I opened the sources.xml-file and found the entries for the mini and the mbp in the

        <path pathversion="1">zeroconf://_smb._tcp.%40local%40minihome/</path>

mbp:(user is mbp15home):

        <path pathversion="1">zeroconf://_smb._tcp.%40local%40mbp15home/</path>

Same result with a mbp with MacOS Big Sur.
Why does the connection fail?

As a guess: one device is WiFi and one is Wired, and your router doesn’t allow mDNS to cross boundaries.

Use a static IP for best results.