@Rusydan (Dan) Thank you for reaching out to us, diagram you mentioned above for Multiple forests (located in China, Singapore, Malaysia) connecting to single Azure AD tenant - Yes, this scenarios is supported and public documented at https://learn.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-topologies#multiple-forests-single-azure-ad-tenant
Is it possible to sync the identity in on-prem AD China to the Global AD tenant? - Yes, this is possible.
Let me know if you have any further questions, feel free to post back.
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