@haroldhongjukoh elegantly explains; POTUS's "withdrawal" from the WHO
is 90% smoke and mirrors, 5% stupidity, and 5% Russian Roulette
Trump's Empty "Withdrawal" from the World Health Organization
...
...
At this moment, it does not appear that Trump has yet sent the WHO
Director General any formal notice of withdrawal. But under these two
congressional conditions, first, the United States remains obliged to
meet its financial obligations to the WHO in full for the current
fiscal year. Second, the United States may not legally withdraw from
the WHO Constitution at the earliest one year until at least from the
date that Trump sends a formal withdrawal notice - in other words,
sometime in mid-2021, at which point, of course, Donald Trump may no
longer be president.
So what does his "withdrawal" really mean?
Not much. First and most obviously, if Joe Biden is elected president,
he need only renounce Trump's claimed withdrawal before it is
scheduled to take legal effect, which would be four months or more
after a President Biden would take office.
https://www.justsecurity.org/70493/trumps-empty-withdrawal-from-the-world-health-organization/