Resizing A Macbook Pro Partition
Unable to perform your specific resize request while busy encrypting

this part indicates me your drive is currently mounted and some write operations are being encrypted to disk.
while encryption of data (write operations) is happening, you cannot resize.
I believe you have three options

If you have an extra drive with a TimeMachine backup, you can delete the volume, make a new partition and restore backup
See this other answer for a hint.
https://apple.stackexchange.com/a/349215/415753
Umount your drive and do offline resize, you probably need to reboot into diagnostic mode.
Disable disk encryption before doing the resize, which is likely going to need to be happening offline anyway.

Note that Offline means not-mounted also known as &quot;while not using it&quot;.
If that's your root filesystem, then you need to boot into diagnostic mode, or with a rescue Live disk.
I believe 1) is the safest.
You should do a backup before whichever options you choose