Resulution

Hi. If you set a 2560 x 1440 (2k) monitor to 1920 x 1080 resolution, will that be the same as an actual 1920 x 1080 monitor? Can you tell the difference between a a 2560 x 1440 monitor set to 1920 x 1080 and an actual 1920 x 1080 monitor? Or will there be a difference like blurry or causing...

So I have had a lot of problems with my new laptop but there has been this one thing that doesn't seem to want to work and it's my resolution, some things say its running at 1080p but my system(not games or web), speccy and https://www.screenresolution.org/ all seem to be saying that it is...