Answer

GTK 3’s Wayland backend doesn’t expose the pointer enter event serials needed for the pointer-warp protocol. The serial values are low-level Wayland details that GTK 3 abstracts away and doesn’t provide in its API.

Your options are:

• Implement a parallel Wayland listener for each surface to track pointer enter serials yourself. This is the only reliable way if you want to stick with GTK 3.
• Migrate to GTK 4, which has better support for Wayland protocols and may expose the serials you need.
• Patch GTK 3’s Wayland backend to expose the serial, but this is complex and not officially supported.

In short, there’s no straightforward way in GTK 3 to get the pointer enter serial. You would likely need a parallel listener or move to GTK 4 for native support.