Are these two the same TV?

Yes. The K-55XR80 is the full model code for the 55-inch BRAVIA 8 OLED. Panel, processor and audio system are the same.

Which has better picture quality?

Neither. Both use the same OLED panel, XR Processor and XR Triluminos Pro. Any difference you read about comes from settings, not hardware.

How many HDMI ports does it really have?

The BRAVIA 8 has four HDMI inputs, two of which support HDMI 2.1 features like 4K at 120 Hz and VRR. Confirm the count on the listing you buy from.

Is it good for gaming?

Yes. 120 Hz refresh, VRR and low input lag suit PS5 and Xbox Series X. The OLED panel gives fast pixel response with no smearing.

Do I need a soundbar?

Not necessarily. Acoustic Surface Audio+ vibrates the screen itself, so sound comes from the picture. A soundbar still adds bass and scale.

They should last the same, being the same set. OLED panels can dim over years of heavy static content; varied viewing and the built-in panel care settings help.

Sony BRAVIA 8 55-inch OLED TV vs Sony BRAVIA 8 K-55XR80 OLED TV

These are the same television: the BRAVIA 8 OLED, sold as the 55-inch BRAVIA 8 and as model K-55XR80. Picture, panel, processor and Acoustic Surface Audio+ are identical, so the choice comes down to the listing, not the hardware. Both carry a 4.7 rating, though the BRAVIA 8 listing has far more owner ratings behind it. Buy whichever listing has the ports and accessories you need confirmed.

Choose the 55-inch BRAVIA 8 if you want the listing with the larger body of owner ratings and a voice remote in the box.
Choose the K-55XR80 if you want the model number spelled out for warranty and support checks and an eco remote in the box.

Prices

Sony BRAVIA 8 55-inch OLED TV: $1,398.00 at Best Buy (last seen Nov 10)
Sony BRAVIA 8 K-55XR80 OLED TV: $1,398.00 at PC Richard & Son (last seen Nov 2)
Difference: both cost the same at the latest prices (Nov 2 and Nov 10)