Hi! Welcome to the forum! 
Is your issue because grub is not running os prober? 
You may try this:
sudo nano /etc/default/grub
Go to the end of the file, and type this in a new line:
GRUB_DISABLE_OS_PROBER=false
Ctrl + s to save
Ctrl + x to exit
Now update Grub configuration:
sudo grub-mkconfig -o /boot/grub/grub.cfg
It may take some time because os-prober is slow. Be patient!