The fact is Microsoft did spent R&D money to support Apple customers, with a product without which, Apple would even be less relevant in the late 90's.

They didn’t do it out of charity. They did it for profit. Microsoft was on the stage when the Mac was introduced in 1984. I don’t think they were ever seriously considering stopping Mac development. They ported office to PPC Macs in 1995 before the joint announcement 2 years later.