Car went into limp mode and won’t go past third, is this electronic or mechanical?

Something strange happened today, I was driving normally when the car suddenly felt like it lost power and refused to shift beyond third gear, just held the revs high and wouldn’t budge. A yellow warning light came on that I think was the transmission one, and the car went into what I assume is limp mode. I pulled over, waited a bit, restarted, and the light stayed on but it drove normally again for a while before repeating. I’ve read reasons an automatic transmission stops shifting explained in a few places now and the causes range from something as simple as a faulty wheel speed sensor confusing the ECU to serious internal damage, which is a massive gap and I have no idea where I fall. My question is whether limp mode specifically points to an electronic fault rather than a mechanical one, because if it’s a sensor that would be a relief. Also is it safe to keep driving short distances while this is happening or am I risking turning a cheap fix into an expensive rebuild? And should I avoid clearing the code myself so a proper diagnostic can actually read it?