A couple of centuries back, wasn't most of the world population subsistence farming in conditions broadly described as serfdom?

Being a subsistence farmer was incredibly risky. One bad year and your whole family starves to death. People only did that because there was no alternative. As soon as the industrial revolution came, people left their "self employment" en masse to work at a company.

That's because it wasn't risky to get a job as a helper to a working professional, learn their trade while doing the worst/easiest part of the work, transition to doing skilled work while having your helpers do the crapwork and the professional did inspection and finishing, then either taking over the shop from the professional, partnering with the professional, or opening your own shop with your already established customers.

So completely unrelated to the modern world.

Self employed in the sense of being part of the gig economy (serfdom), working all day for a modest living under Uber (local ruler of the day). The risk was dying when the next war broke out or it stopped raining for a year.