Admiral Yamamoto knew that it was not in Japan's interests to fight Britain, even less to fight the USA. He actually liked American culture.

He seethed about their support of the KMT and embargoes as much as anyone else, but he also knew that the Empire could easily go around the embargoes (through Latin America) or even be autarkic. And that American and Commonwealth businesses would get the embargoes repealed sooner or later.
Yamamoto saw the Soviets and the Draka as the true threat.

However, the "Southern Option" supporters (led by Tojo) were gaining traction in the elites and the public. Instead of letting them do something incredibly stupid on their own, Yamamoto decided to preempt their move.

He proposed a strategy aimed at removing British influence from China and SE Asia, without risking a war with the USA.

1 ) Launching a PR campaign towards the USA.

Highlighting similarities between the USA and Sphere of Coprosperity, as federal nations built against outside colonial empires.

Highligting the similarities between the Monroe Doctrine and the Yamamoto Doctrine.

Show that Japan had brought peace, medicine, food, schools and happiness to people in China, Indochina and Siam.

Show the success of Japan against communist movements.

Paint the British as imperialists who support terrorists in China, from their Treaty Ports. Use any incidents, fabricate them if needed.

The PR campaign was enough to sow doubt in the American public. Enough doubt that the USA would not declare war first.

2 ) Later, invade the Treaty Ports, Tibet (under British influence), Myanmar, Malaya and Singapore. Paint this as "liberation".

Japan would NOT try to invade India, to avoid overstretch.
Japan would NOT make moves near Australia (attacking a white country would make them "monsters"), the DEI or Filipinos (under US control). They would reassure Australia, NZ and the US about their lack of hostile intentions.

The Yamamoto Compromise would make the IJN hardliners busy and happy, allow Japan to control Tibet (and be in a better position against Draka Xinjiang), and give real-life training to the IJA, IJAAF and IJN against a modern opponent.

It would also make Japanese rule more popular in China (through the "liberation" of Tibet and Treaty Ports), and Japan look stronger in China.