Mobile devices, unless you get really close to the screen, have matched the retinal density for a while. Most people hold the device at about 8 inches, so 450 dpi is the value to hit.
Edit These measurements assume 20:20 vision, which is the average. Many people exceed that. So you'd need slightly higher values if you're feeling pedantic.
100 dpi with subpixel rendering already maxes out angular resolution (horizontal). It doesn't max out everything (retinal), so you still see some artifacts, but practically this is not that relevant. The price in energy/bandwidth rises quadratic for very little gain.
To get the equivalent of 4K at 100 ppi - with 200 ppi you have to put the burden of 8K onto the GPU... For now this is absolutely not good - High ppi is ok for small monitors and handheld devices, but for a decent desk with several good monitors GPUs just aren't ready yet.
For rendering of text/video even an underpowered integrated gpu can handle it fine, only issue is using a bunch more ram.
For reference my very underpowered desktop AMD igpu on 3 generations old gpu architecture (2CUs of RDNA 2) only has trouble with the occasional overly heavy browser animation