Is this route okay?

Yes, this route is perfectly eligible for 144 hours visa free transit in wider Beijing area (consisting of Beijing, Tianjin and Hebei province).

However, you have to be aware of the following:

- Your flight Seoul - Beijing cannot have any additional landing within mainland China
- Your flight Beijing - US cannot have any additional landing within mainland China and South Korea

If your itinerary complies with the above mentioned criteria, you will be eligible for 144 hours visa free transit.

My flight from Beijing to USA does have a layover in South Korea. Thinking I could buy a flight from Seoul to Japan (FUK airport) then to Beijing. The trip with layovers would be: USA > Korea > Japan for a day > Beijing > Korea for layover > USA. Could this work? It's my only option as I do not have time for a visa. Thanks

Japan - Beijing - Korea is fine if you have no other landings in China Mainland.