I remember thinking the same thing when I first setup with Proxmox but then I read a technical post somewhere regarding the way linux and vm display memory usage. I’m going to butcher it, but essentially it said the memory usage displayed in the promox gui didnt reflect actual usage within the VM (cache, etc). While the memory was actually being reserved in the host system (my case a Nuc with 16gb of Ram), within the VM itself, there was likely a lot of “available” memory. Comparing the Proxmox gui versus the HA systemmonitor, it appeared to true.
I allocated 4gb to my HA instance:
But HA reported a lot mor memory available:
I could never truly get my head around memory usage in Linux, but this felt right 