Bootloader bootet direkt zu manjaro

Das müsste bereits gemountet sein und du kannst unter /boot/efi darauf zugreifen.
Das geht z.B mit:

sudo ls -lA /boot/efi/**/*.efi                                 
-rwxr-xr-x 1 root root  278528 25. Jun 2020  /boot/efi/EFI/boot/bootx64.efi
-rwxr-xr-x 1 root root  282624 26. Jun 2020  /boot/efi/EFI/manjaro/grubx64.efi
-rwxr-xr-x 1 root root  116147 13. Sep 20:29 /boot/efi/EFI/refind/drivers_x64/btrfs_x64.efi
-rwxr-xr-x 1 root root  317712 13. Sep 20:29 /boot/efi/EFI/refind/refind_x64.efi
-rwxr-xr-x 1 root root  927680 31. Mai 2021  /boot/efi/EFI/tools/Shell.efi
-rwxr-xr-x 1 root root 1029696 31. Mai 2021  /boot/efi/EFI/tools/Shell_Full.efi
-rwxr-xr-x 1 root root 1366584 29. Okt 13:25 /boot/efi/EFI/tools/shellx64.efi

Switch from Windows:

Provide Information:

Dual Boot:

If this option is set to ‘countdown’ or ‘hidden’, then, before displaying the menu, GRUB will wait for the timeout set by ‘GRUB_TIMEOUT’ to expire. If ESC or F4 are pressed, or SHIFT is held down during that time, it will display the menu and wait for input. If a hotkey associated with a menu entry is pressed, it will boot the associated menu entry immediately. If the timeout expires before either of these happens, it will boot the default entry. In the ‘countdown’ case, it will show a one-line indication of the remaining time.