Part of the reason there is some confusion is the term pre-dates the Marxist use of the term, which Lenin originated. Just like how imperialism was a term, but Lenin used it to refer to a specific phenomena of capitalism. In fact I think he originates it in Imperialism the Highest Stage of Capitalism (though he might have used it earlier, I can’t remember)

The original term in the late 19th century was just used for a well paid worker. This is what a whole heap of non-marxist people still use.

The IWW started using it in the early 20th century specifically to refer to professionals like engineers, doctors, skilled craftsmen, who were insulated from the same conditions as other workers. Who would often have guilds, rather than unions. The IWW specifically being Anarchists, Syndicalists, Marxists, DeLeonists and other various socialists, but not Marxist-Leninists. So you also hear it used in some union contexts still. Not that the IWW really is around in any real numbers, but it sort of spread to less radical unions.

Then Lenin uses the term to apply to all workers in the imperial core as is mentioned in other comments here. Despite myself holding to the Marxist-Leninist position I have basically dropped it from my vocabulary due to the ambiguity. I will say well paid proletariat, or imperial core proletariat etc