Are you doing it from a localscript in StarterPlayerScripts? They run really early, so you may need to wait a little in order to give the corescript enough time to set itself up. The corescript is what disables the topbar, so if it isn’t listening yet, disabling the topbar wouldn’t work.
I finally got around to checking it out and I’m not sure it solves any real issues. It’s not that bad to call pcall repeatedly until it works. If I added a signal, it’d also need a way to check if it’s already happened in case your script runs late. There’s not really a pleasant way to write this… except maybe a yield function that only yields if it needs to…
The worst thing is when you teleport into a new subplace and your topbar flickers because you had to wait a frame before the corescript initialized. I’m convinced that we can easily fix this on the corescript side instead of the c side.