Taiwan is not a member of the WHA because Taiwan is not an internationally recognized state. This is an issue that the WHO has no control over. It's a body tasked with coordinating public health around the world, not with solving intractable disputes over sovereignty and diplomatic recognition. I thought that the particular interview you linked to was done in very poor taste. The interviewer was trying to force someone who focuses on public health to make a statement about territorial sovereignty. She should ask politicians that question, but trying to promote Taiwanese sovereignty by bashing the WHO is just very low. Public health is something incredibly important, and shouldn't be made into a political battleground or damaged for cheap political points.
https://www.discovery.org/human/2020/04/20/taiwan-didnt-trus...
The WHO person in the interview could have responded to the second question on how Taiwan was handling it. Just responding with "China is doing great in all regions" is just a big fucking joke. If you don't think so then it's clear what kind of person I'm talking to.
https://www.ft.com/content/b59c238c-d004-44a2-bd9f-c5b1e7a5b...
And by the way, the WHO doesn't even recognize Taiwan as shown in this very painful video.
https://youtu.be/fASh2_RzMuE
So yeah, my opinion is that the WHO can go screw itself.