When it comes to partitioning, Gparted is very good.
As per your individual problem, perhaps it may give you some hints and ideas.
With that being said, the first thing I would do is do a Timeshift save before doing anything else.
Yes I have tried. But the problem is not the tool , problem is to "how". As gparted also parted doesn't let you create new partition or split it if there is no other free space for partitioning in the system.
Gparted is not the same as parted, which sometimes comes installed on your distro.
Do you have Gparted-live installed on a flash drive?
It would help also, if you could give some information about your computer.