Can I buy Elements 2021 in China ?

Just to add to Phil's informative reply, if you go to the Elements free trial page that he linked, you can change the region of the webpage by clicking on the globe icon at the lower left of the page.  Since I don't speak Chinese, I have no idea whether any of the language choices in the lower right of the screen might be helpful.  I checked out the Hong Kong region and was unable to find any availability for Elements there.  As Phil suggests, the resellers in China may only have the ability to sell Creative Cloud licenses.  Each region is different.

There are quite a few Chinese Adobe Gold & Certified Resellers. I can't guarantee they sell to individuals or that they even sell Photoshop Elements (I think they will concentrate on Creative Cloud products), but it's worth checking with them.

Adobe Partner Connection Portal

Another option might be if you are near an Apple Store. The physical version of Photoshop Elements is both Mac & PC. Again, I'd ring ahead first to check. Ditto for the Microsoft Experience Stores.

I'm not sure if the online Microsoft Store or Apple's App Store are available in China, but if so, you might want to consider their respective store versions of Photoshop Elements 2021.

Amazon (China) is selling Photoshop Elements 2021 via Amazon (Germany). You might be waiting for a while for it to clear customs though.

If all these options don't appeal to you, you could get a trusted family member to purchase Photoshop Elements with your credit card direct from Adobe's website (using your Adobe ID) in your home country. Then if you login to your Adobe account, you (should) be able to download the application and enter your serial number. I'd try downloading the free 30-day trial first though, just to make sure that none of the required Adobe services are blocked in any way.

Download Photoshop Elements free trial