I'm testing antiX 13.2 in a VM, but i cannot get a resolution higher than 1024x786 and the Auto-resize Guest Display option is grayed out. Any ideas tyo solve this issue?

you need to install the virtual box guest additions. There is a virtualbox menu option you can click to insert the guest additions iso. this will show up as a cd in the guest OS. from there, you run as root VBoxLinuxAdditions.run and it will install the kernel modules required for more resolutions, among other things.