Should I rebuild my old portfolio in the same repo or start fresh?

If the main goal is learning, I’d keep the project in one repository and put the React app at the root. Move the old static site into a clearly named folder so the build setup and package files stay straightforward. That also makes it easy to compare the two versions.

A separate repository is cleaner if you expect the two versions to be maintained or deployed independently. You avoid mixing dependencies and build configuration, and each project is easier to understand on its own. The tradeoff is that their histories won’t sit together in one place.

Branches are a good fit if the old version is mainly something you want to preserve, not keep developing. Leave it on a legacy branch, then rebuild the current version on your main branch. Git keeps the earlier work without needing a second copy of the files in the project.

I’d decide based on how you want to work with the old site later. If you’ll actively update both, separate folders or repositories make that clearer. If you just want a reference copy, a branch is simpler. There isn’t a special React requirement here, so pick the setup that will be easiest for you to run and explain.