I just send you a PM with some screenshots regarding point no. 2 of your post and the "edit" part also ... Good luck ...
yes, thanks - it works now
for everyone else with the same "issue" (in English):
1. go to Windows 10 device manager (right click "This PC" > Properties > Device Manager)
2. you'll see "Android Phone" there (on top), and under it - "LG Android Interface"
3. double click "LG Android Interface", select update driver
4. select "Browse my computer for driver software" and on the next page
5. select "Let me pick from a list of available drivers on my computer" and on the next page
6. select "MTP USB Device" > click "next"
7. driver should be updated and installed
now the phone is visible under "Portable devices" in device manager as "LG-D80x" and you can browse its internal storage with Windows Explorer
thanks to @theelderstatesman for the guide and screenshots he sent via PM