can I force my Mac to upgrade from Catalina to Big Sur or a newer OS

If your Mac is not compatible with anything later, you can’t ‘force’ it to upgrade.

There are hacks out there that claim to allow you to do so, but you’ll end up with an unsupportable mess that does not perform as expected.

There are some things that you can get to prolong the useful life of a computer running Catalina.

Free and Open Source Software

• If you need a newer Web browser, download a third-party Web browser such as Firefox . The current version of Firefox runs on Catalina and is still getting updates.

• If you need an office suite, or would like another one, download LibreOffice . The current version of LibreOffice runs on Catalina. Microsoft has a policy of supporting only the most recent three versions of macOS, so I don't think you can still get a version of Microsoft Office that runs on Catalina in a supported fashion.

• GIMP (GNU Image Manipulation Program) is a Free and Open Source photo editor. As far as I know, Adobe does not support Catalina any more – so if you want a photo editor with advanced features like layers, to supplement the Apple Photos program, GIMP, Affinity Photo V2, and GraphicConverter are the main games in town.

Commercial Software

• Carbon Copy Cloner and SuperDuper! are two good utilities for making backups, including bootable backups of your startup drive. You should be making backups (using Time Machine and/or one of these programs), and it's also a good idea to have an external startup disk on hand (clone backup, or clean installation of macOS). While there is Internet Recovery, if you're running an old macOS, it's best not to put all of your eggs in that basket.

• Affinity Photo V2, Designer V2, and Publisher V2 will run on Catalina. As will GraphicConverter, a photo program from another vendor.

It simply doesn't contain the hardware required to run a newer version of macOS.

Scottish blood. Still have family there. Live in the US, though.

No. Technology advances, new versions of software are written to take advantage of it.