Your builder gives you an .ipa file, and Apple expects it to be uploaded from a Mac. You don't need one. I set up a small workflow in your own private GitHub repository: it runs on GitHub's Mac servers, checks the .ipa with Apple's tool first, uploads it with Apple's own upload tool, then deletes the key from the server. Your App Store Connect API key goes into your GitHub secrets, so I never see it.

How it goes:

I send you the workflow file and step-by-step notes for creating the App Store Connect API key (App Manager role; the Account Holder or an Admin creates it) and adding it to GitHub. That part takes you about 10 minutes.

We run the first upload together in writing: you press "Run workflow" and send me the run log (GitHub hides your secrets in it), and I fix anything Apple's check flags.

After Apple processes the upload, the build shows up in App Store Connect under TestFlight. Every next update is a new .ipa and one click.

You need an Apple Developer account (Apple charges USD 99 a year), an app record with the same bundle ID as your .ipa, the .ipa itself and a free GitHub account. If the .ipa isn't signed for the App Store, Apple's check says so before anything is uploaded.

$60 to $90 fixed for the workflow, the guide and the first upload together. Later updates and App Review questions: $30 a month.

Does GitHub charge for this? GitHub Free includes 2,000 Actions minutes a month for private repositories, and Mac minutes count about ten times faster. Without a payment method on file, GitHub stops the run instead of charging you. Does it submit the app for review? It uploads the build. You pick it in App Store Connect and submit it for review there, and I can walk you through that.

This is the upload method Apple documents, and to be upfront, I haven't done this upload for a client yet. https://flowlab-dev.github.io/n/ipa-to-app-store/

Tell me which builder made your app and whether its record already exists in App Store Connect, and I'll send the plan for your app.