After installing Kubuntu, grub shows a black screen and doesn't detect Windows dualboot

Prior to installing Kubuntu I had a Ubuntu and Widnows10 dualboot.

Since I installed Kubuntu in place of the Ubuntu I noticed that grub didn't show up and the new OS would boot automatically. After opening grub customizer I see that the Boot default entry was set after 0 seconds. Changed that to 4 seconds in hopes it would show up. Now it shows a black screen for 4 seconds after proceeding to boot Kubuntu (which would be its first item on its list).

Here's the other issue. Nowhere in grub customizer's boot list do I see Windows, BIOS does not see it as a bootable either.

lsblk outputs:

sda      8:0    0 119,2G  0 disk 
├─sda1   8:1    0  47,7G  0 part /
├─sda2   8:2    0   7,6G  0 part [SWAP]
├─sda3   8:3    0    33M  0 part /boot/efi
└─sda4   8:4    0  63,9G  0 part /home
sdb      8:16   0 931,5G  0 disk 
├─sdb1   8:17   0   931G  0 part 
└─sdb2   8:18   0   529M  0 part

sdb is where windows is stored, specifically sdb2 should have been bootable. I don't know much around this and I would greatly appreciate any help/explanation. Thank you in advance.

After updating grub I still get the same output.