So, as I said in post #6, this can happen because the website "responds" to the perceived screen resolution, and this is not as simple as it seems.
So, it's normally a function of this, not the manufacturer of the computer.
On tablets and phones, the ability to "read" the screen resolution is a little more straightforwards, it is more complex, and subject to "misinterpretation" on PC's and Macs.
A good example is a person on a PC who has a nice 24" monitor with a "native" resolution of 1920 x 1080, BUT!! that user has adjusted the "magnification" in the display options to 250% for example.
Not all software correctly reads this... I have several applications that go nuts on my 4k screens with 150% magnification...
I'm not an expert on Macs, so do not know the exact menu to change the "apparent resolution" (as the real native resolution of the LCD never changes).
So, I think this is what you are seeing...
For the record, I read this forum on 5 different Windows 10 computers, all with different screen resolutions (3 laptops and 2 desktops).... no full page ads, but I guess I need to log out and turn off my blockers.
Greg