This is not the PR preview

Netlify's automatic deploy-preview-N-- URLs are intentionally disabled.

That automatic build runs without the per-PR backend URL, so it would point at the production backend. Logging in there would operate on production data.

Use the per-PR preview instead — the pr-N--rsm-studio-frontend.netlify.app URL from the PR's Preview Deploy comment. That one is wired to the PR's own backend.