Since in latest version of SPFx 1.19 node 16.x was deprecated

I guess it makes no sense in giving the option to support that in our scaffolded flows since those commands target latest version of SPFx.

We should remove the following logic

and

Also in order to make the flows more reusable we should extract the Node versions to variables with default values so that if needed it should be easy for the developers to adapt the pipeline to desired Node version.
We should update the JSON definitions of the flows here

By adding to them variables for Node.js versions that will be used in the flows with the default value set to node 18.x

for example for Azure DevOps pipeline we should add something like

variables: [
...
    {
      name: "NodeVersion",
      value: "18.x"
    },
...

and then modify the NodeTool step to

            {
              task: "NodeTool@0",
              displayName: "Use Node.js",
              inputs: {
                versionSpec: "$(NodeVersion)"
              }
            },