With OEM Windows, everything can be expected, from bloatware "drivers" slowing down your machine by half to obligatory root certificates (thanks Lenovo! thanks DELL!) that are necessary to serve you in-browser ads. And you're not theoretically allowed to remove them or it voids you warranty. So an ad at startup doesn't surprise me, it's not really Microsoft's fault, but that's what you get with a Windows OS.
https://www.extremetech.com/computing/218437-dell-laptops-ma...