Providing release details is always helpful, as it lets us know what software stack (esp. what versions of software you’re using), and for installs the ISO used also matters, as we respin ISOs which may also mean the version of installer varies too.
The software will examine the hardware it sees, and give what options it considers available for that given hardware. Where windows systems may exist or any OS where an unclean file-system is detected, some options may not be offered until you resolve the detected issues/errors (eg. disable hibernate or fastboot that causes the unclean state, or perform file-system checks if the unclean state was because of actual errors)
On some problematic hardware I have had strange errors that vary on the install media (including different versions of installers including ubiquity but also very much calamares). On such devices, I prepare my partitions before I start the installer, then start the installer and use it only to select the prepared partitions rather than using the installer to make those partitions. This is particularly useful on devices that are non-standard, be it unusual/abnormal setup (non-PC type device) or really old short-term devices that were made only briefly using spare parts etc (ie. the manufacturer took shortcuts that reduced their time & saved them money)
All our products are tested extensively; seen Testing Checklist - understanding the testcases or on the ISO QA tracker.
FYI: Attempting to install on a system with 7.4GB of space I see as a user-procedural error. Ubuntu Desktop has recommended a minimum size of 25GB since Ubuntu 17.10, and whilst we at Lubuntu haven’t provided minimums since mid-2018, I’d expect users to know their hardware pre-install, but maybe that’s just me.