The Proxmox Virtual Enviroment (PVE) is a opensource hypervisor using Linux KVM and has support for containers and ZFS, Ceph and more.
In order to get updates for the PVE 6.x (and you do not have a subscription) you need to add this line to your "/etc/apt/sources.list"
deb http://download.proxmox.com/debian/pve buster pve-no-subscription
Then use this to update (or the UI), if you need updates for version 5.x replace "buster" with "stretch" (all versions).
apt update apt dist-upgrade
To get a better network performance, especially between your VMs, you should set the MTU. Open "/etc/network/interfaces" and add this to your vmbr to enable "jumbo frames"
bridge_ports enp1s0 pre-up ip link set enp1s0 mtu 9000
Don't forget to reboot and setup your VMs with the same MTU.
For LXC Containers take a look here.
PCI passthrough (Intel)
Replace at your "/etc/default/grub" the "quiet" in line with
And do "update-grub"
Add to your /etc/modules
vfio vfio_iommu_type1 vfio_pci vfio_virqfd
After a reboot it should work. Check it with "dmesg | grep IOMMU"
[ 0.000000] DMAR: IOMMU enabled
If you get the following error in "dmesg" set "intel_iommu=pt"
[fault reason 06] PTE Read access is not set