How to get into Boot Manager?

Question

Windows

I'm trying to install Ubuntu next to Windows 10.
I can't get into Boot Manager - I already turned off fast boot and pressed different keys (F2, F12, Del). But nothing helps.
What is the problem?
Lenovo V580c Win10

Answer 1

Good evening.
If you are talking about the ability to choose which system to load, then grub recovery will help you

Answer 2

Disconnect the laptop from the mains, disconnect the battery, open the cover on the back of the beech and pull out the battery (round), wait 15 minutes. Bios should reset reset. Further on the manual.

Answer 3

This is a fresh hornbeam bug, or rather a hole in the developer's memory, but there is a working solution:
sudo nano /etc/default/grub
Manually add the line below
GRUB_DISABLE_OS_PROBER=false
Ctrl+O, enter, Ctrl+x
sudo update-grub
reboot