There’s an extensive description for ‘More RAM’ in Pi-Apps (under ‘Tools’).
Not really spent much time with anything other than Pi OS on my Pis so far. I tried out Ubuntu but don’t see much reason to switch. VMWare ESXi looks like an interesting one to try out though.
You can even boot the Pi 5 by USB now (as standard), so you don’t necessarily even need to fiddle with micro-SD cards to try it. [Edit] Actually, I’m reading that maybe you need UEFI firmware to be loaded on a micro-SD, while booting with the ISO on a USB drive, for setup.
It also appears that the available ISO is from 2020, requires a Broadcom account, is labelled as experimental, and allows a 180-day trial period only. [/edit]