Need serious help [90% of the pages I view give a URL not found error]

New to this forum, so hello you Macreatures!
Alright lets get to business -
I own am iMac and for a few months now I've been dealing with this weirrrrrrddddd issue:
For some reason, about 90% of the pages I try to view online send me back an error message saying "not found. The requested URL was not found". I get this message on A LOT of webpages, on YouTube videos, almost 8 times out of 11 I'd get this message.
It only happens on my iMac. Every laptop or smartphone won't have any issues so I know the problem must be with the computer.
Any professional experienced and patient help would be sooooooo appreciated!!!!!!!

Thanks you guys.

checking my ip

Thanks - can you brief me quickly on what exactly this means and how I do it? again - sorry for all the trouble, i'm a genuine idiot when it comes to tech stuff.

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thanks for the link you posted but unfortunately it didn't help