Thanks, just what I was asking for.
I must admit, though, that I'm no expert in reading the DxDiag output. But sometimes it's enough to read it through to see any oddities like the one I found on the second instance of Nvidia RTX 3070:
Current Mode: 1920 x 1080 (32 bit) (300Hz)
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Monitor Name: Generic PnP Monitor
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Native Mode: 1920 x 1080(p) (60.054Hz)
There might be a natural explanation for how a 60Hz monitor could be driven at 300Hz but that's beyond my knowledge. That said, Alienware have made the m15 R4 with both 144Hz and 300Hz monitors so that might explain.
Resetting the Nvidia settings might be a good start: Open the Nvidia control panel, go to Manage 3D settings on the left and click the Reset button. Further, in the Program Settings tab add aceshigh.exe, no need to adjust any settings in the box below. Then go to Change Resolution in the left pane and check that the Refresh rate is within reason. It doesn't have to be the maximum, I've set mine to 120 for my 144Hz monitor to reduce the load on my video card so it both runs cooler and keeps the fps steady.