This is exciting to see as arm64 is really a growing space, as we've seen since first launching our Docker image build acceleration [0]. Free for public repos is definitely a strong pull if you can live with some of the quirks.
Even with this, building multi-platform Docker images with fast persistent caching in GitHub Actions will still be slow in the worst case and tedious in the best case.
We've also expanded into GitHub Actions runners, bringing our fast caching and faster compute into the actual runner.
We've done some cool things like making caching and disk access faster using ramdisks, Ceph, and blob storage [1]. We're offering Intel, ARM, and macOS runners at half the cost of what GitHub offers to private repos. We're also focused on accelerating even more builds outside of the runner. [2]
[0] https://depot.dev/products/container-builds
[1] https://depot.dev/blog/introducing-github-actions-ultra-runn...