@ZeteSP,  @HelpFixDecoApp,

Just to clarify, CGNAT vs. public IPv4 assignment is determined by the ISP, not the router. Deco Mesh (and other consumer routers) don't generally have a setting that allows you to switch between CGNAT and a public IPv4 address―the router simply uses whatever WAN IP address is assigned by the ISP.

That said, Carrier‑Grade NAT is widely used by ISPs and usually doesn't impact standard browsing or speed tests. However, CGNAT can affect certain use cases. These can commonly include things like port forwarding, inbound connections, some VPN configurations, online gaming NAT types, and remote access in some scenarios.

As for why performance improved after switching to a Public IP...

In some cases, moving off CGNAT can resolve ISP‑side issues like congestion, routing inefficiencies, or other traffic behavior occurring upstream of the home network (e.g., on an ISP-side gateway that's shared among numerous customers). If any of these were happening upstream while under CGNAT, you may see improved real‑world performance by switching over to a Public IP. Just keep in mind―this change occurs on the ISP side, rather than due to any router configuration or behavior.

Since you've already taken the recommended step to resolve this behavior (contact your ISP to ask whether a public IPv4 or IPv6 connection is available), you should be set.

Hope this helps!