MacOS – Cannot resize APFS partition – “The new size must be different than the existing size”

The GUI for Disk Utility has always had problems with resizing volumes.

You could try diskutil from the command line, if you trust your skills enough.

I'd start the Terminal and write diskutil list to see all devices connected.
To resize a volume from the list you'd write something like this (Let's assume that disk2s2 is 100GB):
diskutil resizeVolume disk2s2 50g HFS+ Lion 0b

This should create a secod partition with 50gb size, HFS+ format(mac format) and the name Lion

The HFS+ volume data structures "know" how big the volume is; this means that if you take a 159.2 GB HFS+ volume and edit the partition table to make it 815.8 GB, you now have an inconsistent state: the partition table says its 815.8 GB, the volume data structures say it's 159.2 GB, and any tool that looks at both is going to be confused.

To avoid this problem, do not use gpt to change the size of partitions that contain HFS+ volumes, and don't use dd to clone between partitions or disks that aren't exactly the same size. Instead, change partition sizes with with either diskutil resizeVolume or Disk Utility (these edit both the partition table and volume data structures to keep them in sync). Also, you can clone HFS+ volumes with either something like asr --source /dev/disk1s2 --target /dev/disk2s2 --erase (note: verify /dev entry names are correct before entering this command!) or with Disk Utility's "Restore" tool (these both correctly handle expanding/contracting HFS+ volume data structures to match the target partition).

At this point, I'd erase the new drive and start over -- it's easier to use the right tools from the beginning than it is to clean up after using the wrong ones.