@BoomUK55
Welcome to HP Support Forums. A really great platform for posting all your questions and finding solutions.
I understand that you are having problems using the bottom 2 HDMI ports on your computer.
I'd like to help.
Please Note that your computer comes with the Radeon RX 580R (4 GB) Graphics Card and Integrated video is not available if a graphics card is installed.
The 2 bottom HDMI port are integrated by default on the Motherboard and hence wont work since you are using a Graphics card

Hope this helps. Keep me posted if you need further assistance.
Thank you 🙂
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KrazyToad
I Am An HP Employee