stirl: here is my grub config: https://pastebin.ubuntu.com/p/4NbhhPNQjr/
yours should look similar after running the grub makeconfig command thing. 
the important bit is the menuentry at line 96. 

root=PARTUUID=blah line might not be necessary. but i did that in my /etc/default/grub because i was debugging the issue with mounting root which turned out to be missing initrd line. so, make sure you have that initrd line after the linux line. i didn't but maybe its becaue im dumb at dracut or something. idk. grub is weird and i dont fully understand it yet