hello, i don't seem to be able to update my OS X version 10.13 to macOS Big Sur !! i couldn't find it in the apple store
That's odd. Can you open the App store from your Dock or the Applications folder and search for Big Sur? It should be the first result.
Provided that your Mac is in the list of compatible computers you can get information on the Big Sur upgrade from here which has a link to the App store page here.
when i click on it , i get transferred to the apple store and it says " cannot connect to apple store "
..There are a few other support sites with additional links such as..
• How to get old versions of macOS - Apple Support
Has more info and cross-reference to newer and older build models
to include Big Sur reference/link; with Catalina, Mojave, High Sierra,
El Capitan; and links concerning hardware that can be helpful, too.
Good luck & happy computing!
The trick is to use your Safari browser to click on any links the redirect you to the App Store.