Hello,

Exactly, as written in the documentation, to do this you must also respect these two conditions:

a) The empty space must be located on the disk drive immediately after the volume that you want to extend.
b) There can't be any volumes between the volume to extend and the empty space to add.

That's why you need to repartition "disk 0" causing that the "in between" allocated partition to be moved after the unallocated space.
As I told you, there are several (third-party) tools capable of doing this, some "free" (like gparted) others "commercial" but I can't recommend any of them in particular because I haven't had to use them for several years.

Regards,
Ferdinando