Mac bock 13" 2011

You can install 10.13 High Sierra on a 2011 MacBook Pro, but you need a 2012 on newer MacBook Pro to install 10.14 Mojave.

Mac OS 10.13 is available at no charge. This Apple article has a link to it:

How to get old versions of macOS - Apple Support

Find the "Download macOS" section and the ink to High Sierra is there.

TWO NOTES:

• Use Safari for any downloads There are plenty or reports that FireFox is not working correctly when downloading mac OS installers
• If you get an error about a file being damaged, all that means is that the installer you just downloaded has found an older, invalid version of itself in your Applications folder Delete the old version, empty the Trash, and you can proceed.

As per macOS Mojave - Technical Specifications:

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen and choose About This Mac. These Mac models are compatible with macOS Mojave:

• MacBook (Early 2015 or newer)
• MacBook Air (Mid 2012 or newer)
• MacBook Pro (Mid 2012 or newer)
• Mac mini (Late 2012 or newer)
• iMac (Late 2012 or newer)
• iMac Pro (2017)
• Mac Pro (Late 2013; Mid 2010 and Mid 2012 models with recommended Metal-capable graphics cards)