if wan block ads, can try Pi-Hole or setup as local dns (so no need remember ip addresses).
add few hdd then can run TrueNas as NAS, can setup SMB shared folders or backing up VM, or iSCSI allow for other pc to install game on it, then if there are some storage space left unused can try StorJ or Chia Farming for passive income (bad thing is the payout is in their own crypto token, so need find ways to sell the token).
if u r programmer can try CodeServer, is VSCode on browser can code on any devices.
if u r gamer, can try setup remote gaming vm by adding GPU and pass through the GPU, install parsec then can game remotely. or if u have nvidia 1000 or 2000 series card, can try vGPU to create multiple gaming vm with 1 gpu.
HomeAssistant if wan play around smart home.
these are what i can think of currently, of course there are many others thing u can do with proxmox, u can google if need more ideas, and here the link can help to create vm/container easily and also other useful tools for proxmox:
https://tteck.github.io/Proxmox/about port forwarding, im using unifi which they have changed mine to private ip address, so port forwarding no longer work for me, im unsure about Maxis Fibre. the work around currently im using is ZeroTier so i can access to my vm from outside, ZeroTier is more like vpn.