Same error here.
This would happen on any apt update call after adding the repo.
$ sudo apt update
Hit:1 https://nvidia.github.io/libnvidia-container/stable/deb/amd64 InRelease
Ign:2 https://isaac.download.nvidia.com/isaac-ros/release-3 noble InRelease
Err:3 https://isaac.download.nvidia.com/isaac-ros/release-3 noble Release
404 Not Found [IP: 93.184.215.166 443]
Hit:4 http://security.ubuntu.com/ubuntu noble-security InRelease
Hit:5 https://download.docker.com/linux/ubuntu noble InRelease
Hit:6 http://us.archive.ubuntu.com/ubuntu noble InRelease
Get:7 http://us.archive.ubuntu.com/ubuntu noble-updates InRelease [126 kB]
Hit:8 http://us.archive.ubuntu.com/ubuntu noble-backports InRelease
Reading package lists... Done
E: The repository 'https://isaac.download.nvidia.com/isaac-ros/release-3 noble Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
$ sudo grep -r nvidia /etc/apt/sources.list
deb https://isaac.download.nvidia.com/isaac-ros/release-3 noble release-3.0