Everything that doesn't have a discrete GPU has unified memory these days. If you're asking for something closer to the RTX Spark or Apple Silicon then look at AMD's Strix Halo systems.
Also, if you'd like to know of an earlier example, the very first Raspberry Pi has fully unified memory. Released 2012, SoC from 2011. It's not exposed in the usual APIs which is why you have a configurable RAM allocation for the GPU, so you need to write special code targeting the GPU cores. You can pass a pointer from the CPU and have the GPU read data directly. Results are written back to RAM which can be read by the CPU.
The M1 isnt particularly good at inference, so pretty much every major current competitor with a 256+ bit unified memory system is better: AMD Strix Halo, NVIDIA DGX Spark, possibly Intel Panther Lake
Even in Apple land M1 isn't the first with unified memory - pretty much all intel on-chip GPU (Sandy Bridge and newer) count - it was even a reason for driver issues early in intel's new dedicated GPU lineup, as the drivers expected unified memory - but M1 is essentially modification of an iPad chip, and you can see "unified memory" there going all the way back to first chip Apple bought from Samsung to power iPhone 2G
You were likely only using Intel systems then. AMD systems have had iGPUs capable of light gaming for a very long time. It took Intel a long time to get to that level, after M1 (2020).
You are missing a major detail: integrated GPUs are crap. They win on efficiency but not on raw compute. Before AI (and crypto too, I guess) people bought GPUs to render graphics and that was their main consumer. People built more and more demanding games that required increasingly powerful GPUs to render well. Gaming systems always had a discrete GPU so there was no reason to scale up integrated GPUs because they wouldn't sell, or they would be a waste of die space.
I don't think the M1 specifically focused on inference. Their goal was to replace Intel/AMD/Nvidia with their own chips, and since the previous Macs shipped discrete GPUs, they had to match or beat those so they don't ship something slower.