Click,Click,Click!

You need to make tests UNDER LOAD, that is with the starter attempting to engage. Example is a battery cable corroded inside so that it's effectively a no14 wire instead of a no4. it will operate the dome lights and radio, etc, but not the starter. Clip your meter directly onto the starter "big" terminal and a good engine ground. Be careful, as of course, the large terminal is full battery power. Jumper the starter relay and see what it reads. Should have at least 10V or more

If so, then could be starter relay, wire between relay and starter solenoid, or starter

If not, then something in the main battery cable

Now clip onto the starter small terminal. Jumper the starter relay. Should have full 12V there. If not, then, starter relay, or that wire between them.

If you have full battery voltage there, and at the starter "big" terminal as well, then I'd say .....starter....