I found that switching between other distributions can better be done in a separate partition. One extra thing to do, though, is that some OS's like Ubuntu only autodetect other OS's like Windows and show these as options in the bootloader screen, but they don't do the same for other Ubuntu-like OS's like Kubuntu. So to get the options to boot into either Ubuntu or Kubuntu (or others) if you have both installed, you need to add the following line to /etc/default/grub and follow the instructions to run update-grup:

GRUB_DISABLE_OS_PROBER=false

EDIT: forgot that I may need to run the following too afterwards, from the OS to be considered the main OS:

sudo dpkg-reconfigure grub-efi-amd64-signed