Four choices on one wizard tab decide whether Windows 11 installs cleanly or refuses to start. Here is what each one actually does, in plain words.
Most failed Windows 11 installs on Proxmox die before the first setup screen - killed by a setting on the System tab of the Create VM wizard. BIOS type, a tiny EFI disk, a TPM checkbox and a machine model: each takes five seconds to set, and each is painful to fix afterwards. This page explains all four honestly.
SeaBIOS is the old-style legacy BIOS. OVMF is a real UEFI firmware for virtual machines, and it changes what the VM can do: UEFI boot, Secure Boot support, and disks over 2 TB. Windows 11 officially requires UEFI, so a Windows 11 VM on SeaBIOS fails its requirement checks before setup even starts.
Choosing OVMF adds one duty: you must also tick Add EFI Disk. That small disk stores the UEFI variables - without it, the VM has nowhere to remember its boot settings. For Windows 10 and Server guests SeaBIOS can work, but there is no prize for staying legacy: OVMF works for all of them and keeps your fleet uniform.
Windows 11 setup checks for a TPM 2.0, and a fresh VM does not have one until you add it. In the System tab, tick Add TPM, choose your storage, and set the version to 2.0. Proxmox emulates the TPM in software - no physical chip is needed on the server.
Be honest with yourself about what the TPM holds: its state is stored in that TPM disk, and features like BitLocker inside the guest tie themselves to it. Back that disk up with the VM and never casually delete it, or the guest may treat the machine as changed hardware.
The machine type is the virtual motherboard model. i440fx is the ancient, maximally compatible board; q35 is the newer model with a PCIe bus instead of old PCI. For a new Windows VM, q35 is the sensible default - it is what current Proxmox versions suggest for Windows, and it is the friendlier base if you ever try GPU passthrough later.
The honest part: q35 does not make Windows magically faster. Day-to-day speed comes from VirtIO drivers and CPU type, not the board model. What q35 buys you is modernity and fewer dead ends. What you should not do is flip the machine type on a working VM for fun - Windows sees a motherboard change and may re-check activation and drivers.
Keep the SCSI controller as VirtIO SCSI single. It is the fastest controller Proxmox offers for a single disk, and the single variant gives the disk its own IO thread option later. While you are on this tab, tick Qemu Agent as well.
That tick only tells Proxmox the agent will exist - the agent itself is software you install inside Windows with the guest tools. Ticking it now saves a confusing mismatch later, when Proxmox waits for an agent that was never announced.
Watch the video to see these exact System tab choices being made while the Windows VM is created.
Watch Full VideoYou can add a TPM device later, but you cannot fix the BIOS afterwards - a Windows installed under SeaBIOS is a legacy-boot install. If you forgot the TPM, add it and reboot; if you picked the wrong BIOS, it is cleaner to recreate the VM with OVMF, an EFI disk and TPM 2.0 from the start.
Not in any way you would feel. The honest gains come from VirtIO storage and network drivers, CPU type set to host, and enough RAM. q35 is worth choosing for new VMs because it is the modern PCIe-based board and the better base for passthrough - not because of speed.
Deleting the EFI disk removes the VM's UEFI boot variables, so it may stop booting until repaired. Deleting the TPM state makes Windows treat the machine as changed - BitLocker recovery and activation checks can trigger. Treat both small disks as part of the VM and back them up with it.