After updating my TV (OLED65GXPUA) on August 31, 2020 the HDMI-ARC volume support changed: pressing the volume up/down button once on the magic remote will continuously apply volume changes until the volume has reached the maximum or minimum value. Prior to this update volume changes over the HDMI-ARC interface behaved as expected: one press of the remote button would apply one increment or decrement to the volume. A Klipsch Bar 48 is attached to the TV over the HDMI-ARC interface.
After the update the TV is running: webOS TV version 5.1.1-3701, Software version 03.10.41. I do not have the version information prior to the update.
