You don’t need a static IP.
You need a „publicly routable IPv4 address“ from your ISP. No need for it to be static.
Your server should have an IP reservation within your home network. While I recommend using a manual port forward (as it gives me a little more control), others have their remote access setup working just fine with UPnP.
Some other common causes for having issues with your remote access could be an issue your home network setup (e.g. „is your Nest directly connected to the internet or is there some other router/modem?“).
