Apple does not use off the shelf PCIe NVMe SSDs. The "rules" you've internalized from PCs do not apply.
Apple integrates their own SSD controller directly into the M-series SoC. It connects to the internal "Apple Fabric" bus that links CPUs and high bandwidth peripherals to DRAM.
This SSD controller connects to flash modules over standard x1 PCIe links, one per module. (No, it's not a proprietary offshoot of PCIe,
@deconstruct60, please don't confuse things like you so often do. Lots of your post up there was just nonsense.)
An Apple flash module is several flash memory die packaged together with a PCIe-to-NAND bridge IC designed by Apple. These bridges are not full SSD controllers - they don't implement the flash translation layer which does all the LBA-to-physical mapping and wear leveling. They just make it possible to read and write flash memory over PCIe.
The number of x1 PCIe lanes available for flash modules depends on which SoC you have. For base M1/M2/M3, it's 4 lanes (so, 4 modules maximum). For M1/M2/M3 Pro/Max/Ultra, it's 8 lanes, or 8 modules maximum. This means Apple already has the potential for SSD throughput equivalent to Gen5 x4 M.2 SSDs - gen4 x8 is the same bandwidth.
Getting angry because Apple hasn't jumped on PCIe gen 5 yet is silly. There's not much market penetration of gen 5 yet, and the most important thing which might make use of it (GPUs) isn't a big deal on Apple Silicon since Apple has chosen to not support third party GPUs.
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