Put default values inside the ! list; put the :cb outside the quotes (maybe); give a value (even space) to every variable (sometime is useful);
yad --form --scroll --width=800 --height=800 --center \
--field="Distro Name Enter Name of your Distro" "$distroName" \
--field="Source Partition Enter the source partition. For Example /dev/sda1" " " \
--field="Filesystem Please select filesystem to format drive":CB "${Pippo}!ext2!ext3!ext4" \
--field="Output Drive Please select drive to write ISO file":CBE "${Pluto}!sdc!sdd!sde!sdf" \
--field="Format Partion":CHK "$enablePartFormat" \
--field="Output Partition:NUM" "$partNumber" \
--field="Add Boot Flag to Partition":CHK "$bootFlag" \
--field="Install Penguins-eggs":CHK "$installEggs" \
--field="Use eggs squash":CHK "$eggsMkSquash" \
--field="Install eggs Calamares":CHK "$enableEggsCalamares" \
--field="Install Standalone Calamares":CHK "$enableinstallCalamares" \
--field="Live ISO Prefix Name" "$isoPrefix" \
--field="Live ISO Basename" "$isoBaseName" \
--field="Use ISO Compression":CHK "$enableIsoCompression" \
--field="Type ISO Compression":cb 'xz!gzip!squash' \
--field="Modify eggs mksquashfs command:TXT" "$mkSquashCommand" \
--field="Modify eggs xorriso command:TXT" "$eggs_xorriso_cmd" \
--field="UserName" "$userActName" \
--field="UserPassword" "$userPW" \
--field="Root Password" "$rootPW" \
--field="Grub Menu Name" "$grubMenuName" \
--field="eggs Compression":cb "Standard!Max" "$eggsCompression" \
--field="chroot for Finalization":CHK "$enablechroot" \
--field="Install Grub":CHK "$enableInstallGrub" \
--field="Install Grub to Device":cbe "/dev/sda!/dev/sdb!/dev/sdc!/dev/sdd!/dev/sde" \
--field="Mount Grub Install Partition to /mnt":CHK "$mountGrubDevice" \
--field="Grub install method":cb "sudo grub-install /dev/sdx!sudo grub-install --root-directory=/mnt /dev/sdx" \
--field="update configuration":CHK "$enableUpdateGrub" \
--field="Grub update method":cb 'sudo update-grub!sudo grub-mkconfig -o /mnt /dev/sdx \#must mount device /mnt' "$grubUpdateMethod" \
--field="Regenerate Kernel image":CHK "$enableRegenKernelImage" \
--field="Install kazam Video Record":CHK "$installKazam" \
--field="Install gnome-terminal":CHK "$installGnomeTerm" \
--field="Install mousepad":CHK "$installMousepad" \
--button="Exit:1"