While that'd be enough for only the packages of Proxmox VE itself, the installer creates a partition for SWAP and also some parts of the disk space for a LVM-Thin, so you either need to force those to something smaller or zero (avoid using zero for SWAP), that can be done in the options on disk selection, or better in general:
Use a bigger disk, 8 GiB is really not much for a hypervisor OS. With that small space you'll continue to run into issues with updates and the like.