1. What make and model is the new TV?
2. What does the Roku Ultra say in its Settings -->Display Type section?
Mine says "Detected: 4K HDR 60hz HDCP 2.2".
You might need to enable a setting on your TV like "Deep Color" or some such to get 4K and/or 4K HDR on that particular HDMI port. So, report back on the Display Type and make/model of TV.