This is interesting insight, would you care to share some parts of your ssh config indicating how you use ssh over a proxy here, most likely through a VPN?
ProxyJump is to connect to one SSH server by another SSH, right? It doesn't work against GFW. GFW throttles SSH traffic across borders to ensure that SSH can only be used for running commands rather than tunneling data.
Yeah I assumed that's what you were doing, since you mentioned Github blocked specifically. If you need to proxy through a protocol other than SSH, likely need to keep using ProxyCommand.