Setup iommu

First, if you don't know how to use "vi", why are you not using nano like with the other file?
Saving the file with vi is "ESC ESC :wq". Or just use nano to edit that file: "nano /etc/modules".

And are you sure you installed Proxmox with grub bootloader? Because the screenshot shows that you are using UEFI and not BIOS. If you are using UEFI you are probably booting from a EFI partition and not from a GRUB bootloader and in that case you are editing the wrong files. In that case you should follow the instructions for "systemd-boot" and not for "grub".