How to get rid of DOUBLE dual boot screen

Hello all!
I have installed Ubuntu20.04 and Windows10 OS on my laptop. The problem is that I don’t know the right way to get rid of one out of two dual boot screen. Each OS displays their own dual boot screen and I want just one. Last time I had tried to solve this problem, I caused fail in booting Ubuntu 14.10 in a way that mbr file was corrupted and couldn’t repair it by no means, so that’s way I seek help this time.
Important BIOS settings are adjusted as follows:
a) boot mode is on LEGACY
b) fast boot option is OFF

I would appreciate any useful advice. Thanks in advance!

You could use bcdedit and a admin command prompt to set the timeout “bcdedit /timeout 10”. If you
set this below 5, something will not boot.

I also have two boot prompts, one with Grub and one with Windows, Windows is set at 10 seconds,
unless I hit the enter key. Grub is booting Mint and it is the OS I boot unless I boot Windows.