New to SilverStripe, and I have to say a pretty abysmal start.
Out of the box, on fresh install of 2.4.5, I can't even upload a 20kb jpg.
Did a search on the forums, seems to be a whole slew of similar problems dating back as far as 2 years ago.
Could not find one answer that worked.
Yes, assets/uploads folder has the correct permissions.
I have other systems on this same server, Wordpress, Drupal, Concrete all with zero issues uploading files of any type.
Again, pretty abysmal!