I don't know why, I am now in Chinese mainland, where several brands of mobile phones can't open itch with their own browsers and independent official browsers. I have tried many mobile phones and many browsers, but only the browser of vivo brand mobile phones can open official website normally. What's the problem?

Have you heard of the Great Firewall of China?

https://en.wikipedia.org/wiki/Great_Firewall

Wikipedia is also banned there, so you’ll need the same method you use for accessing Itch.io to read wiki entries.

https://en.wikipedia.org/wiki/List_of_websites_blocked_in_mainland_China