Lenovo Z580: can't boot from USB or access BIOS

Hello,
I'm trying to clean install Windows 10 on my laptop but I'm having some problems.
My laptop is an old Lenovo Z580 i7. Initially it had Windows 8 but then I somehow managed to clean install Windows 10 on it.
I said somehow because I'm trying to do the same right now, but I can't manage to do it!
The problem is I can't find any way to boot from USB to access to the Windows 10 installer. It's a well known problem with Lenovo Z580 that many people had. When I clean installed a couple of years ago I managed to boot it from the USB, but I tried so many things now and I can't do it!
I tried clicking the Lenovo button (which is how it's supposed to work) but nothing happens. I tried to access the BIOS but it doesn't let me go on it, whatever button I press on boot. I tried to reboot from Windows 10 going on Settings -> Recovery, still I can't get to boot via USB.

Does anyone have a suggestion about what to do?

Thank you.

You can do it without even booting from a flash drive using a little known trick as shown here first afaik by user @Kari.

Shrink C drive partition by about 5 GB.

Create new partition in unallocated space and assign drive letter eg D

Download iso to D.

Mount iso as a drive, and run setup.exe from the sources directory - not setup.exe in root of mounted drive.