How to setup Solo2 for DVR?

You bought a device from 2012? Send it back as long as you can… If it was cheap and used, it is a maybe. Still, such an old device won’t give a lot of fun.

To use it with plex you need to install HRTunerProxy on your Solo2:

DL @ GitHub - OpenViX/HRTunerProxy: Setup Enigma2 to act as HR-Tuner Proxy

Dunno if it will work with your Methusalem.
The STB will then appear as an HDHR device for Plex.