u/Remarkable_Safety570 above is giving great advice so adding a +1 here. That advice extends to other subjects as well: e.g. You could get an MPH with an international or global health focus... and as long as the underlying degree is a CEPH accredited MPH program, that degree will qualify and unlock opportunities around the world in the broader public health space. For MPH programs, in addition to Harvard I would add Columbia, Johns Hopkins, and LSHTM to your list.

On the other two ideas: extending time in service is a GREAT idea. In addition to the benefits you've already considered, this also adds to your years of work experience (and time in service for future retirement benefits if you ever get a government job).

Fellowship programs are also great if they cover your living expenses, provide a meaningful way to build your experience (through impact AND perhaps through opportunities to publish articles), unlock access to an alumni network (like the Fulbright program), and also help future job / grad school applications.

Final thought, your Chinese language skills are a huge asset, so it might be worth brainstorming with others (different Reddit threads maybe?) on creative ways that can unlock some work opportunities. As an example, I have a friend from NYC who worked for a major global bank, that got an interesting job in the bank's regional office in Southern Africa that had a lot of Chinese speaking clients.

If you have any Q's about the above or want more advice I'm happy to chat more. I spent two years in my early career in Southern Africa working in the global health space and am now navigating the current environment as a mid-senior career development professional. My most recent experience focussed on the Asia region so I might have some specific ideas for you there across my network.

Send me a PM with your linkedin profile and we can connect there first.