Rubio said arrangements for a meeting between Putin, Trump and Xi at the APEC summit are ongoing. It's not 100% finalized yet.
The Americans want to discuss with China and Russia the issues of limiting nuclear weapons. China is unlikely to agree to the restrictions, as they would consolidate its backlog of nuclear warheads and delivery vehicles from Russia and the United States, while China seeks to move closer to leaders on this issue.
The Americans are clearly unwilling to recognize China's right to possess a similar number of warheads and delivery vehicles, although China does not actually need American approval to pursue this. The rule is no.