Install PureOS without Ethernet at hand

I want to install PureOS on one notebook, but I have no ethernet at hand. Only WiFi.
I have:

  1. PureOS on an USB
  2. USB with all non-free Debian drivers.
  3. WiFi Dongle with MediaTek MT7610U chipset which is supported on Linux in the Kernel.

I booted the PureOS Live USB.
As expected no WiFi adapter recognised.

I plugged the WiFi Dongle. It gets recognised in lsusb. But I still have no WiFi option in the Gnome Settings.

I plugged the USB with the drivers and tried with sudo apt install ./firmware_iwBlaBlaBla.deb and got an error message:
Download is performed unsandboxed as root as file … couldn’t be accessed by user ‘_apt’. -pkgAcquire::Run (13: Permission denied)

Any ideas?

I could set up a Raspberry Pi 4 as a router and use its Ethernet port to provide Ethernet for the notebook, but I was hoping for an easier solution utilizing either the internal WiFi of the notebook or the WiFi dongle.

sudo dpkg -i xyz.deb


The WiFi is working now. The secret was in:
sudo modprobe -r iwlwifi
sudo modprobe iwlwifi