The IBM PC that debuted with the 286 was the PC/AT ("Advanced Technology", hah) that is best known for introducing the AT bus later called the ISA bus that led to the proliferation of video cards, sound cards, and other expansion cards that made the PC what it is today.

I'm actually not sure there ever was a "true CPU computer age" where all processing was CPU-bound/CPU-based. Even the deservedly beloved MOS 6502 processor that powered everything for a hot decade or so was considered merely a "micro-controller" rather than a "micro-processor" and nearly every use of the MOS 6502 involved a lot of machine-specific video chips, memory management chips. The NES design lasted so long in part because toward then end cartridges would sometimes have entirely custom processing chips pulling work off the MOS 6502.

Even the mainframe era term itself "Central Processing Unit" has always sort of implied it always works in tandem with other "processing units", it's just the most central. (In some mainframe designs I think this was even quite literal in floorplan.) Of course too, when your CPU is a massive tower full of boards that make up individual operations and very the opposite of an Integrated Circuit, it's quite tough to call those a "general purpose CPU" as we imagine them today.

The C64 had the famous SID chip (MOS 6581) for sound. Famous in the chiptune scene at any rate. https://en.wikipedia.org/wiki/MOS_Technology_6581

The C64 was discontinued in 1994 but is technically still available in 2021 as the C64 Mini. ;-)

The C64 mini runs on an ARM processor, so that doesn't count in this context. Also I just learned that the processor in the C64 had two coprocessors for sound and graphics (?). So maybe that also doesn't count.