EveryCircuit for absolute beginners. Actually a simulator rather than a schematic tool like KiCad/Altium. The advantage of EveryCircuit is that it animates current flow, which can be helpful when understanding the very basics. I'm surprised that it hasn't been mentioned yet.

I do believe though that as of writing, the user interface for EveryCircuit is quite "janky" (it actually drives me nuts) compared to CircuitLab which actually my current favourite simulator.