Asus X299 TUF mk1 couldn't install Proxmox right away.
So, after installing Debian 10.4 Buster, add proxmox repository and install it to work.
1. Skipped how to installing Debian 10.4 buster and set static ip address
2. add repository like this with root account
nano /etc/apt/sources.list
deb http://ftp.debian.org/debian buster main contrib
deb http://ftp.debian.org/debian buster-updates main contrib
deb http://download.proxmox.com/debian/pve buster pve-no-subscription
3. update a repository even if error msg found that proxmox repository
4. install wget and gnupg2
apt install -y wget gnupg2
5. download and add a key.asc
cd /etc/apt
wget http://download.proxmox.com/debian/key.asc
apt-key add key.asc
** this command should be running on the /etc/apt path.
6. download gpg file
wget http://download.proxmox.com/debian/proxmox-ve-release-6.x-gpg -O /etc/apt/trusted.gpg.d/proxmox-ve-release-6.x.gpg
7. install a proxmox and other pkgs
apt update
apt install proxmox-ve postfix open-iscsi
then reboot your system will working that proxmox perfectly!