You cannot append released windows disk space directly to your Manjaro partition.
While you may be able to merge released space to the west of your Manjaro partition - it requires you to be booted on a live ISO as you cannot modify a mounted partition - and more importantly you may - for a newcomer too high a risk - be left with an unbootable system.
The reason is the complete rewrite of the root partition which in many cases modifies the GUID of the partition.
Know your system beforehand - is it MBR or GPT partition schema?
The fail safe method is to release the space in Windows - then boot your Manjaro system and create a new partition using the free space.
Then proceed to create a mount unit for the new partition to mount on a dedicated folder - e.g. /data/games or /data/private (Don’t create beforehand - the mount unit will take care it that). Remember to change permissions on the mounted partition as the defaults is root owned and readonly to everyone else.
Learn how to do this by reading this guide
If you are familiar with mount units you jump directly to the topic on sample mount units