As far as I understand, Stallman is not supportive of promoting or using the term, but he does not disagree with the OSI’s definition.
But I quite often see trolls trying to claim that he does, since if the term is disputed, it opens up for what the trolls really want to do, which is always to illegitimately market their proprietary software (with abominable license terms) as “open source”.
1. Calling proper nomenclature “gatekeeping”.
2. Selectively quoting people to seem like they disagree, where in fact no such disagreement exists.