OK you need to be specific with what you are trying to acheive. When I use windows for example I need to use VM and Ubuntu to use DFU to program the stm32. Once this is done I don't really need it the rest can be done within WSL.
You should not need to install the bootloader as it comes preinstalled installed, however if you do then installing bootloader In Ubuntu terminal running under VM:
sudo dfu-util -s 0x8000000:leave -a 0 -D output/mystorm.raw -t 1024
Make sure when you plug the BIMx into usb to hold the Boot button down whilst connecting, this ensures that the BIMX powers up in DFU mode (normally led red). After stm32 is programmed, disconnect BIMx and shutdown Ubuntu VM you should be finished with it.
In WSL whenever you plug in the BIMx setup the serial/usb port by issuing:
sudo stty -F /dev/ttyS3 raw -echo
You can then upload a binary to the board using that serial port (led green):
cat trail/chip.bin >/dev/ttyS3
I am using '/dev/ttyS3' here because BIMx comes up as com 3, your com port number may differ (have a look at device manager serial/usb ports) e.g. com 4 would be'/dev/ttyS4'
If you want your FPGA design upload to be permanent, you can switch the BIMx into flash mode by a single press of the mode button (whilst powered up and plugged in) which makes the led yellow. Now when uploading to the tty it copies to the flash also and remains there after power down.
Doers that help?
Oh BTW this is the getting started guide which has some additional information, you normally get this in a email link on shipping. The firmware and some examples can be found in the IceCore repository on github. For the BBC stuff probably best to post under those relevant threads in the forum and the folk interested in the Beeb stuff will likely be notified and perhaps comment etc.. but make sure the basic stuff is working ok first and you are familiar with BIMx general operation before tackling the more complex Beeb/Atom stuff..
Oh and welcome BTW