Starting with Sparky 7.0 “Orion Belt”, the default configuration of GRUB bootloader does not “see” other operating systems as default.
To fix that do:https://wiki.sparkylinux.org/doku.php/grub_does_not_see_other_oses?do=edit
If the grub config file does not exist, copy it, as root:
sudo cp /etc/default/grub.ucf-dist /etc/dafault/grub
Then edit it, as root, using any text editor, for example nano:
sudo nano /etc/default/grub
adding the following line:
GRUB_DISABLE_OS_PROBER=false
on the end of the file.
Then update grub:
sudo update-grub