Please don’t start multiple threads with the same questions (PBC = xy slow performance).
Have you checked the MD log files? Check what you are offloading to GPU. It’s possible that some interactions can still not be run on GPU with walls. Bonded interactions should be possible since 2024.1 (Performance improvements - GROMACS 2024.1 documentation), but there might still be other things that cannot be offloaded when using walls.