· Neither my phone app nor my tablet app can find the Roon server even though it is connected to the ethernet from the same router. The server is accommodated by a Trigon Exxceed device. I have installed the latest version of the app and restarted the Trigon several times. Did not help.
Is Roon Server actually running on the Trigon Exxceed? Can you confirm this?
Since Roon 2.65, the minimum system requirements have changed for Linux, and it is possible that the Exxceed is running old binaries for glibc and OpenSSL. You may want to reach out to the manufacturer and share the release notes.
After reviewing your system information, we can confirm what mjw suggested — your Trigon Exxceed is running Linux 4.15 with an older glibc version that no longer meets the minimum system requirements introduced in Roon 2.65.
Since the Trigon Exxceed is a proprietary third-party device, we unfortunately have limited ability to assist with updating its underlying system. We strongly recommend contacting Trigon directly