QUIC still works fine on GrapheneOS. GrapheneOS only removed a way to ask the OS to close a QUIC connection automatically in case the app dies, etc. It's an optimization from a server perspective since it avoids the server thinking the connections are still open and keeping resources assigned to them until the idle timeout it has configured followed by having to go through a connection shutdown process. It's not an optimization from a client perspective.

GrapheneOS also has fixes for around 5 other VPN leaks and more fixes on the way. Android currently implements VPNs in a way that's prone to leaks due to VPNs being per-profile but profiles not using their own network namespaces yet and also depending on central services for the DNS resolver and various other things which have to properly handle VPN support. We have plans to improve the VPN architecture in the future to make it very resistant to leaks. There will also be support for running apps or groups of apps in VMs which can have even stronger protection against it.

This is the path for the graceful closing on the QUIC connection via (IMO) illegitimate/exploitative call, GOS is not disabling QUIC as a whole.

QUIC as it is is brilliant, and this is not a feature of the protocol, it's a feature of the surveillance OS (Google's Android).

Other than that I checked on the OS before the latest release, and it didn't work anyway.