Sorry, I meant to say the ISO was prepared the same way to USB for Knoppix. I just applied the Ubuntu MATE ISO to that same key I used for Knoppix 9.1 DVD image, after wiping it and using rufus 4.11 for the same. The system gets to Grub then reboots, no error displayed this time. I do not have any writable optical media to apply the image to.
Then, maybe while creating the Ubuntu MATE ISO image, something went wrong. Did you try wiping it and creating it again?
Another option is that the Ubuntu MATE ISO you downloaded is corrupted, maybe try downloading it again?
Sorry to insist on this, but this kind of error message displays when there is physical damage, either on the drive or in the ISO image, or while creating the ISO image. You say it worked with the Knoppix image, so I guess the drive is fine.
Rufus is an app that allows you to reformat the ISO during its write, which is done via options in the rufus menus. A consequence of providing this (esp. with Ubuntu releases >20.04) is that your rufus app needs to be updated for later ISOs, so is your rufus version capable of writing 24.04 ISOs?
The rufus docs do refer to this, and suggest writing ISO without change (ie. using that option where all details come from within the ISO itself rather you selecting them), though note I'm not a rufus user and thus it'll use different language (no doubt) to what I've used. I think it calls the clone or unchanged mode dd-mode.
Was your rufus updated? OR you wrote the ISO unchanged to your thumb-drive? as if it was an outdated version of rufus & you selected non-standard options (for a Ubuntu 24.04.3 ISO) that maybe your issue as stopping at grub (or failing to boot correctly) can occur.