Memory usage of Guest, reported once Guest Agent VirtIO Balloon driver/service is installed, is memory used from point of view of the guests not from point of view of the host.
Cached memory in the Guest is really reserved on the host, cannot be shared.
This metric helps to decrease or increase...
updated mass storage driver is displayed directly, but as mass storage is in use, reboot is required to apply.
btw, virtio driver can't fix backend storage too high latency.
from Shell :
lvcreate -l 99%FREE --poolmetadatasize 1G --chunksize 64K --thinpool local-lvm00 pve
then add it from Datacenter \ Storage \ Add \ LVM-Thin ( ID = name can be custom but local-lvm00 prevents confusion )
Try to boot in safe mode to compare Memory , try to disable all startup apps to dig out.
6 GB memory is too low for Windows 11 and many apps. 8 GB is the minimum , 12-16 GB is many apps running , many files used.