I have been struggling to dual boot Ubuntu 18.04 with Windows 11 in my Asus TUF A15 laptop.
Earlier I had Ubuntu 20.04 and Windows 11 (dual-booted, both installed in the SSD) on my system, but then recently I needed to get some work done which was only possible through Ubuntu 18.04. I searched online and found that we can have 2 Ubuntu versions on a single system. So I tried installing Ubuntu 18.04 on my HDD (since the SDD didn't have that much free space) from a USB. After installing, it showed that it had been installed correctly and that I needed to restart the system. After I restarted, in the grub boot loader, it showed Windows boot loader, Ubuntu 20.04 and Ubuntu 18.04 While windows and Ubuntu 20.04 loaded correctly, Ubuntu 18.04 was unable to boot and it showed some errors in the grub screen.
So I thought that maybe if I uninstalled both 20.04 and 18.04 versions and tried reinstalling only Ubuntu 18.04, it may work. So after backing up my data from Ubuntu 20.04, I deleted the disk partitions, boot loader entries and the EFI entries of both these versions.
However, now when I boot my system, Windows boots correctly, there are no Ubuntu entries in the UEFI settings also but in the "Boot from device" option it still shows Ubuntu even when no external USB is connected. If I click on this option, Windows loads.
When I tried to install to install Ubuntu 18.04, I am unable to do so. It still installs correctly at first and after restarting, upon selecting Ubuntu in the grub boot loader, it doesn't boot and shows errors.
