Even if you don't buy from China directly, you can't prevent local brands outsourcing their production, because all of them do It.

This is entirely untrue. Almost anywhere you live in the U.S. you can find local brands with local production.

Where can I find an oven made with entirely US parts (or even ~85-90%+)?

I'll tell you in advance that I haven't been able to locate one in a few years of looking. Most major appliances are, at best, 60-80% american with no accurate accounting, even if they're "assembled in the USA". Cars are the only thing with accurate sourcing labels due to legislation.

Entirely US parts is a very high bar. Isn't it the final product design and assembly that counts in the end? If China has a comparative advantage making resistors, who cares, let them.

And the local production is an assembly of something really made in china.