I have a macOS High Sierra Version 10.13.6. Could I upgraded to macOS 10.15 Catalina?

The version running now is not a factor in what you can upgrade to.

The particular Mac model and year is what determines your available upgrades.

Here are the models that can upgrade to Mojave:

…macOS Mojave - Technical Specifications

Here is the app store link for the kit:

….https://apps.apple.com/us/app/macos-mojave/id1398502828?mt=12

Have a complete and current backup prior to performing the upgrade, if your Mc is supported with Mojave.

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

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 required update or upGrades to 64 Bit Versions.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation

The latest version of MacOS is Monterey (12.0.1). Catalina is 2 versions old. Have you determined what the most recent version of MacOS your Mac can run is? This Macworld article will help you determine how much further your Mac can be updated https://www.macworld.co.uk/feature/what-version-macos-compatible-3776008/. If you click on the Apple logo on the menu bar and then click 'About this Mac', under High Sierra it states the type of Mac you have, the processor type and the year of manufacture. You can then use that article to ascertain whether your Mac is capable of running Monterey. There is a way of obtaining older versions of MacOS, but you should always install the latest for security reasons.