unable to update my OS from High Sierra

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

macOS Catalina 10.15 hardware requirements

macOS Mojave 10.14 hardware requirements

macOS High Sierra 10.13 hardware requirements

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina, Big Sur & Monterey supports only 64 bit and there is no workaround.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may require an update or upGrades to 64 Bit Version

How to upgrade to macOS Monterey - Apple Support

Then see: How to get old versions of macOS - Apple Support

Check compatibility.

You're welcome. From the page I linked.

How to get old versions of macOS - Apple Support

I just checked, you can upgrade to Catalina 10.15.7. Be aware older 32bit apps will not run and will need to be upgraded or replaced. You can check which with Go64