If the cassettes are not VHS, then they are probably Betamax, V2000, or Grundig.
You’ll need a working player to match the cassette system. V2000 and Grundig will be almost impossible to find in working order as they died out long before the VHS/Betamax war ended.
The output at the RF socket will be either composite VHF or UHF in one of a number of different TV broadcast standards, such as NTSC, PAL, SECAM, plus a few sub-variants of those and some other systems. Either way you’ll need something to digitise the analogue sound and picture. Although it will give a major loss of quality (on a source which was already low quality) that could just be by using a digital camera recording a TV screen. But the camera will need a TV screen mode to stop it recording black scanning lines
For best results take the tapes and player to a digital conversion specialist. The digital files can then be supplied on a DVD or BluRay disc (or even CD for small files) and are best backed up to Cloud storage