If its only the main OS not responding to SSH and the web portal just disappears after a couple of minutes use, then it might be your router is reusing the IP address linked to Proxmox. Proxmox uses a static IP address, so will not change once set up. Your router on the other hand may re use the address if it was never reserved specifically for the Proxmox machine. In other words, two devices are fighting for the same IP address on your router.
This is what happened to me. Took a while to figure it out until someone suggested checking the IPs and Mac addresses on the router. No issue since fixing it on the router. Just reserve the address on the router, reset the device that is using the same address (if you can figure it out), and reset the router. Make sure you are reserving the address for the correct machine by chcking the Mac address.
Yes, it let you connect devices to your smart home interface, that don't support ZigBee or Zwave, without having to download a 3rd party app. The new protocol Threads also uses Matter for connection.