Seamless Lightroom Catalog Merge

I have two Lightroom Classic catalogs that need to become one, while keeping every edit, rating, keyword, and collection intact.

• Catalog 1: “Omaha26” – 1,030 travel photos on my newer 13-inch MacBook Pro.
• Catalog 2: “Main” – my full archive on an older 15-inch MBP that can no longer run the latest macOS or Lightroom Classic, so its catalog cannot be opened—or upgraded—on the newer machine.

My idea is to start fresh with a new catalog (“Main 2026”) on the 13-inch MBP, then bring both existing catalogs into it. I have an external hard drive available for shuttling the data, and I want every bit of metadata and every develop adjustment preserved. I’m not sure whether any collections or smart collections need extra care, so I’ll lean on your guidance there.

What I need from you
1. A clear, step-by-step workflow for creating the new catalog, upgrading the old one if necessary, and performing the two imports so nothing is lost or duplicated.
2. Tips on using the external drive for temporary transfers and any recommended folder structure changes to avoid broken links.
3. Verification steps I can follow to confirm that all edits, keywords, and collection memberships made the jump.
4. Advice on cleaning up any orphaned previews or backups once everything is consolidated.

If screen-sharing support is part of your service, let me know; otherwise thorough written instructions are fine. I simply want to end up with a single, healthy Lightroom Classic catalog on my newer MacBook, with zero loss in image quality, edits, or organization.