Since Airbnb is international, I guess if someone (assuming it's a small private operation) is offering rental service there, they might as well setup a proxy for foreign guests.
> Some solutions would sort of work, but unreliably, with extremely minimal bandwidth and would suddenly stop working after some time
The sad part is, anti proxy technology is also fairly advanced. Most of well-known VPN protocols such as OpenVPN, AnyConnect, IPSec and Wireguard etc can be identified via traffic analyze, once GFW detects suspicious traffic, it may launch probes to further investigate the service. That's why Chinese people use Shadowsocks, Clan and V2Ray, those proxies are designed to protect itself from these situations.
Shadowsocks and V2Ray require some know-hows to correctly setup. Notably, Shadowsocks requires AEAD ciphers to be relatively safe, and you should never run Tor through it due to flaws in it's transport protocol. As for V2Ray, avoid VMESS protocol since it's is known to be vulnerable to probe attacks.
DNS pollution was for sure only one means of the blocking. Even if the IP address of the site got resolved correctly, the site could not reached as a result of "Connection reset" or "Remote host closed the connection" errors. I thought the blocking was all the time and everywhere until I accidentally realized that I had just access some site without VPN connected and such state could last for from hours to days, as long as I did not access contents deemed sensitive, sites did not seem to matter that much as blocking would not be triggered until I clicked some links. HTTPS did not seem to help at all, so GFW must have the ability to do deep packet analysis. Such behaviors make sense to me as the network traffics in China are enormous even the government would not have enough resource to monitor everything all the time, so the practical approach would be using a little bit of heuristics and commencing blocking only when certain signals were triggered. Also I encountered a couple of times man-in-the-middle attacks as I noticed my browser were not happy with the site's certificates. Such attack might be carried out by the ISP as the certificates were self signed.
The sim can be purchased in any convince store in hk without identification.
That's the easiest solution in my eyes.
I believe Google's outline uses it
In the end, I'm not going to try that anymore, I haven't been in China for 2+ years now due to COVID, but next time, I'll hope my server is out of the blacklist again and hope I can access my (self-hosted) emails and other normal services that don't try to evade it.
The student VPN of another Asian university or the employee VPN of a well established company seemed to work last time. Not sure if that can be counted on reliably though...
Japan VPS location worked ok to access European sites, much better than Hongkong based, but I guess thats the peering.
Funnily enough I traveled to another part of China then, and the Airbnb wifi had practically no GFW-type blocking. GFW is made up of local or provider-specific implementations that vary a lot. It was a small, rural town.