I tested two services that supposedly allow you to check if a site is blocked in China. I don’t know with certainty how accurate these tools are in general, but I can say they gave me consistent results for lemmy.ml, hexbear.net, and lemmy.ca. Hexbear and lemmy.ml register as blocked, while other instances go through.

https://www.comparitech.com/privacy-security-tools/blockedinchina/

Results: lemmy.ml, hexbear.net, lemmy.ca, lemmy.world

https://www.vpnmentor.com/tools/test-the-great-china-firewall/

Results: lemmy.ml, hexbear.net, lemmy.ca. Lemmy.world could not be parsed using this tool, perhaps due to not being set to work with that TLD.