Hello franconovik! What are you trying to achieve exactly?
Proxmox VE can work with any GPU that has a Linux driver. However, depending on what you want to do (e.g. sharing a GPU between multiple VMs), it might make sense to prefer certain GPUs over others. You will probably want to install the proprietary Nvidia driver for that GPU, which also supports the RTX A6000. You will probably be interested in reading about NVIDIA vGPU on Proxmox VE.