I want to play my electric piano an old Roland HP-147Re with 5pin midi during zoom calls to teach. I have a IMac and will be buying an audio interface after advice probably a focusrite or I have a non powered Yamaha mixer MG10XU what is my best way to connect and which cable.
I'll give it a try:
If you want to send audio:
Having a external sound card, you can connect the Mono R audio output from the Roland to the sound card and use this sound card as the input device for Zoom. On the audio interface you can also connect a mic to talk while speaking.
For that you will likely need an external sound card, however as this website is not about recommendations you won't get any advice on which one is the best…
If you want to send MIDI
MIDI are only carrying information on which note was pressed, at which velocity and so on. However, it does not carry any sound. You need an expander or a synthesizer to create a sound. With MIDI, you can probably display which keys are pressed on a virtual keyboard on the screen, but for that, you need to know what you want to do exactly. In order to do that, you'll need to get the midi to the computer, which can be done with a midi-to-usb cable.
These questions are far too broad and this is why this attempt of answer is not very specific.