I think a lot of the comments so far have no real evidence to support some of the speculations
RAM usage on htop is shown in binary units Gibibytes and Mebibytes instead of decimal units Gigabytes and Megabytes
- 1 GiB = 29 bytes = 1,073,741,824 bytes
- 1 GB = 109 bytes = 1,000,000,000 bytes
My system has a few modifications from stock Manjaro and has been rolling for over 5 years
$ free -h
total used free shared buff/cache available
Mem: 7.7Gi 538Mi 6.7Gi 4.0Mi 505Mi 7.0Gi
Swap: 3.9Gi 0B 3.9Gi
My partner’s Xfce has not been modified much from standard Manjaro install and has only been rolling for 18 months
$ free -h
total used free shared buff/cache available
Mem: 7.8Gi 493Mi 6.7Gi 57Mi 578Mi 7.0Gi
Swap: 3.9Gi 0B 3.9Gi
Both systems have 8GB (7.45 GiB) RAM installed
So these systems are using approximately 6% of available RAM when booted
But your system is only using about 3.5% of available RAM
I do not think that having a bit more RAM used when OS is first booted will impair performance of Xfce when in use