Moving from MacOS version 10 to 11

Is your iMac a mid 2014 or later model? Models earlier than that cannot be upgraded to Big Sur.

The model year of an iMac is available at Apple menu > About This Mac.

A late 2012 through late 2013 iMac can be upgraded to Catalina 10.15.7 but no later. 

A mid 2014 and late 2014 iMac can be upgraded to the latest version of Big Sur macOS 11 but no later. 

A late 2015 iMac can be upgraded to the latest version of Monterey macOS 12 but no later. 

A 2017 iMac can be upgraded to the latest version of Ventura macOS 13 but no later. 

For all of the above, see instructions in: How to download and install macOS - Apple Support  

A 2019 or later iMac can be upgraded to the current version of Sonoma macOS 14. See:How to upgrade to macOS Sonoma - Apple Support

Possible workarounds for not being able to upgrade...

Possible workarounds for not being able to upgrade...

Mostly you just need a more modern Browser than Safari on Catalina, Mojave, or High Sierra like Firefox or Brave.

https://brave.com/

https://www.mozilla.org/en-US/firefox/83.0/system-requirements/

Firefox 83.0 System Requirements (mozilla.org)

Opera…Thanks

https://www.opera.com/download/requirements

Opera system requirements | Opera

Thanks to dialabrain…

Firefox 115 is now the current version. runs in High Sierra.

119.0.1 is now the current version and requires 10.15 or later.

https://www.mozilla.org/en-US/firefox/new/

Thanks to A Brody, Browsers by Mac operating system…

Browsers by Mac operating system - Apple Community

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/

Thanks to Matti Haveri…

https://discussions.apple.com/thread/254698315?answerId=258771288022#258771288022

LibreOffice 7.0.4 works in macOS 10.11 and 10.14.

https://downloadarchive.documentfoundation.org/libreoffice/old/

Thanks to Servant to Cats…

LibreOffice is up to

• Version 7.5.4 – Requires Mojave or later
• Version 7.4.7 – Requires High Sierra or later
• The LibreOffice site is now offering
• Version 7.6.2 – Requires Catalina or later
• Version 7.5.7 – Requires Mojave or later

Release notes indicate that as of August 2023, new versions of LibreOffice will likely require Catalina or later.

And thanks to VikingOSX…

Let's not overlook SoftMaker's Office 2021 suite which has familiar Word and Excel UI design, and opens these documents in their native formats.

https://discussions.apple.com/thread/254982498?answerId=259270210022#259270210022