You can’t really bypass Vercel cache tags, but for CMS previews in Astro, the best approach is to avoid caching entirely. Use a preview flag (like ?preview=true) and fetch data with cache: 'no-store'. Even better, create a dedicated /preview route with prerender = false so pages are always server-rendered and fresh.
TL;DR:
Use SSR + no-store for previews, cache tags only for production.