I'm in the same situation. Many years ago after my Roku Ultra did an update, it stopped controlling the TV for ON/Off and volume. I've tried everything noted in this thread, nothing has worked. Clearly, there was a 1 to 1 coorelation of the TV controls no longer working and the update. NOTHING else changed. Super frustrating, many years of checking in on the issue and trying different things. Nothing.
My Panasonic Viera Plasma has been a workhorse for me, lasting over 16 years and still going strong. Today, I replaced my Panasonic with a new 2024 Hisense and the ROKU remote works perfect with that TV. Clearly it was some update that impacted the compatibility with these Panasonic's. I'm now repurposing my Panasonic to another room for occasional YouTube streaming via a ROKU stick. Guess what.. That stick device updated (hasn't been used for years) and it also does not control the volume. Something's up, no real fix here. Roku is a great product, just not for these older Panasonic Plasma TV's. Wish (despite the likely few still using one) Roku would get to the root of this issue. I'll check in here occasionally.
