I made a Laravel app as a side project and the final version was 2.6.4
I choosed to rewrite it completely and rename.
I changed blade templating to Vue.js, made a better Model and Controller structure, etc.
Should the new version be 1.0 or 3.0
You should make it 3.0
As it is the same project you've been working on and made improvements in.
As maybe your question or confusion is arising from the fact that you've made a complete re-write. But with projects, it usually happens. A complete re-write is usually marked with a version bump.
If the project, however, changes and caters something else than you begin with.
That project would be named differently and have 1.0 as the version.