[DOCS] Rel Notes about ports change (#3768)

* [DOCS] Rel Notes about ports change

* improved wording

Author: catalinaadam

documentation/docs/release-notes/3.0.0.md

@@ -43,6 +43,32 @@ This rootless setup enhances security by eliminating the need for root privilege
 
 For instructions on deploying rootless PMM, check the [Setting up PMM Server](../install-pmm/install-pmm-server/index.md) topic.
 
+### Internal port changes
+As part of the rootless deployment support, PMM 3 changes the internal ports used by the PMM Server to enabling services to run without elevated (root) privileges:
+
+| Service | Old port | New port |
+|---------|----------|----------|
+| HTTPS   | 443      | 8443     |
+| HTTP    | 80       | 8080     |
+
+#### Impact and required actions
+
+- if you have custom scripts that reference the old internal ports (`443` and `80`), update them to use the new ports (`8443` and `8080`)
+
+- for Docker or Docker Compose deployments, update your port mappings to point to the new internal ports while keeping your external ports the same if desired:
+
+??? info "Docker Compose example"
+
+    ```yaml
+    services:
+        pmm-server:
+            ports:
+                - "443:8443"  # Map external 443 to internal 8443
+                - "80:8080"   # Map external 80 to internal 8080
+    ```
+
+For examples of configuring PMM 3 with Docker Compose, including port mappings, see [Docker deployment documentation](../install-pmm/install-pmm-server/deployment-options/docker/run_with_vol.md) and this [Percona Forum thread](https://forums.percona.com/t/install-pmm-3-using-docker-compose-and-connect-mysql-postgres-mongodb/36457).
+
 ### UI-based upgrades for Podman installations
 
 You can now upgrade PMM Server installations running under Podman directly through the **PMM Configuration > Updates** panel in the UI.