Is it possible to test a multi-platform build before pushing it to a registry?

[jkodroff]

I'm using buildx to create multi-platform builds at Pulumi, e.g.:

docker build \
	-f docker/base/Dockerfile.debian \
	--platform linux/arm64,linux/amd64 \
	. \
	-t pulumi/pulumi-base:3.14.0-debian \
	--build-arg PULUMI_VERSION=3.14.0

I want to test the build containers before pushing them to a registry, but it seems like there's no way to get output usable in docker run. If I use the --load option, I get an error that docker exporter does not support manifests. (I'm figuring that this is not a buildx shortcoming - it's a limitation in docker itself.)

Assuming I understand correctly, I figure I have 2 reasonable options:

1. Build a single platform at a time with --load, test locally, then push, although this leaves me stuck having to create the manifest myself, which buildx does so seamlessly (nice work!).
2. Push to a non-public interstitial registry of some sort (something local or a private Docker Hub repo), pull the images in a later step, test on each platform, then push to our "production" public Docker Hub repos.

So, my questions to the community:

1. Is there another way I'm not aware of that would allow me to build multiple platforms at the same time and test before pushing?
2. If not, is there a better option than the ones I've described above? (If the workarounds described above are how you'd do it, that's also helpful for me to know.)

Thanks so much!