Hi. I doubt the error has anything to do with system requirements, because X3 has very basic requirements.
My guess (and I am pretty confident), is that your server has a firewall or security extension, that does not like the
cURL request made to an external ZIP file from x3_install.php. It's not unusual to block scripts from downloading external resources for security reasons. Of course, the only way x3_install.php can install X3, is to download ... Else you would have to install "manually":
https://www.photo.gallery/docs/setup/installation/
I'm pretty sure this is the case, because firewalls and security extensions will normally just return "500 internal server error" with no other info. If it was a normal error, you would see an error that explained the what was wrong or what's missing.