S-Mode is an appliance mode for Windows that prevents installation of any app not from the Microsoft Store. Disable S-Mode and you can install any application like you’ve always done, including Firefox.

Fedora should play nice with Secure Boot enabled. You also shouldn’t need to do anything with the TPM.

I don’t recall in virt-manager off the top of my head. But if you make changes in the XML of a domain, you do have to shutdown/restart the domain before they’re effective. And just to be safe, I would say to shutdown the domain, then check the XML, then start up again.

You do say you’re just using qemu, so if that’s the case and you aren’t using libvirt in front of it, shutdown the VM, make sure your qemu command specifies an e1000 network device, and run again.

I can check virt-manager when I get some free time this evening, if that’s what you want/need.

You may need to shut down the VM, check the device config to ensure it’s set to e1000, then boot it back up. The PCI ID on your original post belongs to the virtio-net device.

Instead of trying to backport the virtio device drivers to that version, I’d recommend editing the VM to use the emulated e1000 NIC.