Lenovo T490 shut down and will not boot into Ubuntu without using grub2 bootloader from USB

There is a boot loader issue for many Lenovo laptops. I do not know why. Specifically this laptop was stuck trying to PXE boot as seen by many IT professionals.

After messing around a bit, I created a bootable USB and loaded the boot loader on my T490's memory from the stick. It then gives me the option to "boot from next volume" and by selecting this I am able to actually load the Ubuntu OS into memory.

Under what cases would the BIOS not be able to find the bootloader?

How can I install the correct boot loader into the master boot record of my SSD while I have ubuntu booted?

I can see the different block devices with

$ sudo fdisk -l

But I do not see a boot loader.

I suppose I would

1. Create a partition
2. Copy GRUB2 to this partition (I am using Ubuntu 20.04)
3. Restart the computer and point the BIOS to boot from that partition.
4. My problem is solved?

I am not dual-booting because I don't like Windows. At all. MacOS & Ubuntu over Windows every time.

First, boot into Ubuntu.

You can easily install grub from a regular Ubuntu session (not a live session) using the following commands:

sudo grub-install /dev/sda
sudo update-grub

This assumes you have only one hard drive or SSD and that this drive is the default /dev/sda.

As far as I know, grub will not show up when you run sudo fdisk -l. However, you can reinstall grub to the MBR using the commands above. Sometimes a Windows update will erase grub and reinstallation is necessary. In any case, you can boot using grub on a USB so reinstalling grub to the MBR should fix your problem.

You can check that your main disk is /dev/sda by running the following command:

lsblk

Then, the output should look like this or something similar:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 232.9G  0 disk 
└─sda1   8:1    0 232.9G  0 part /

However, if the root filesystem / is mounted on /dev/sdb or something different like this:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sdb      8:0    0 232.9G  0 disk 
└─sdb1   8:1    0 232.9G  0 part /

then you would use /dev/sdb instead of /dev/sda:

sudo grub-install /dev/sdb
sudo update-grub