Ahhhh I see now, that explains it. 😃 Yeah it’s not a bad method if you need to resize a partition in place, but you need to be super careful to restore all the partition parameters like sector size etc. exactly the same. And ofc to restore the previous UUID from inside the partition editor (fdisk or gpt) or with tune2fs -U.
For future reference it’s best to use parted instead, which will take care of everything for you. Best to boot into a GParted live stick for any operations on essential partitions, not to do it on the live system. Same thing for copying partitions, use a Clonezilla live stick. With Ventoy you can make a USB stick with several such tools on it, you just install Ventoy and then drop ISO files on the stick.