I got the 0.3Mb arch .pxe install to boot in Virtualbox!
 

Arch via a 0.3Mb file download? Cool!

Just mkdir .config/Virtualbox/TFTP & mv it there/arch.pxe
Create a new VM with matching name arch & select net as boot device. Boot it. Then simply select a mirror; I used Global


Edit added: but I haven't found any other <distro>.pxe that works! (Anyone know of any?)

I found: https://github.com/netbootxyz/netboot.xyz (scroll down to 1st dl: the 3MB .iso)

Many distros, including Slackware current: dmesg: https://termbin.com/tx07
udevd[317-325]: failed to execute '/lib64/elogind/elogind-uaccess-command' '/lib64/elogind/elogind-uaccess-command /dev/dri/card0 ': No such file or directory