Microsoft recently changed from instructing developers to install Gulp to instead instructing them to install Gulp-CLI. Having both installed may be the cause of your issues.

Try running npm list -g --depth=0 gulp to see if you get a result. If you do then, uninstall Gulp-CLI, uninstall Gulp, an then reinstall Gulp-CLI.

npm uninstall gulp-cli --global npm uninstall gulp --global npm install gulp-cli --global 

Also, the earliest version of the SharePoint Framework that is compatible with Node.js v14.15.0 is SPFx v1.12.1. So please ensure you have a compatible version of the Yeoman SharePoint generator installed. I would suggest trying SPFx v1.13.1 to start. If everything is working, then I would try SPFx 1.14.0.

You can install a specific version of the Yeoman SharePoint generator using this command

npm install --global @microsoft/generator-sharepoint@[version number]

For example:

npm install --global @microsoft/[email protected]

For more information see SharePoint Framework development tools and libraries compatibility | SPFx development environment compatibility.

Finally, Microsoft made several changes to the web part template between SPFx v1.13.1 and v1.14.0. If you use a version of SPFx v1.13.1 or earlier, you may want to use the first couple modules in the Extend Microsoft SharePoint – Associate learning path on Microsoft Learn. The content in the modules of this learning path are currently based on SPFx v1.13.1 so they will more closely match what you will be doing.

Microsoft recently changed from instructing developers to install Gulp to instead instructing them to install Gulp-CLI. Having both installed globally may be the cause of your issues.

Try running npm list -g --depth=0 gulp to see if you get a result. If you do then, uninstall Gulp-CLI, uninstall Gulp, an then reinstall Gulp-CLI.

npm uninstall gulp-cli --global npm uninstall gulp --global npm install gulp-cli --global 

Also, the earliest version of the SharePoint Framework that is compatible with Node.js v14.15.0 is SPFx v1.12.1. So please ensure you have a compatible version of the Yeoman SharePoint generator installed. I would suggest trying SPFx v1.13.1 to start. If everything is working, then I would try SPFx 1.14.0.

You can install a specific version of the Yeoman SharePoint generator using this command

npm install --global @microsoft/generator-sharepoint@[version number]

For example:

npm install --global @microsoft/[email protected]

For more information see SharePoint Framework development tools and libraries compatibility | SPFx development environment compatibility.

Finally, Microsoft made several changes to the web part template between SPFx v1.13.1 and v1.14.0. If you use a version of SPFx v1.13.1 or earlier, you may want to use the first couple modules in the Extend Microsoft SharePoint – Associate learning path on Microsoft Learn. The content in the modules of this learning path are currently based on SPFx v1.13.1 so they will more closely match what you will be doing.