Is jiuzhaigou is open to foreigners again? I will be travelling to china in sept-oct this year.

Yes, it opens to foreigners now.

Are there still any health requirements for foreigners?

In 2021, foreigners needed to meet these requirements:
01. Foreigners who live/work in China and has proof of residence/work.
02. Local Tianfu health QR green code.
03. Visitors from Guangdong province (or have been to Guangdong lately) need to have Nucleic Acid Test made in past 48 hours.

Hi, there is not any health requirement at present. However, booking tickets on line in advance is necessary as there is no ticket counter at the spot now. Pay attention that you should enter the scenic area between 7:30-14:00.