Hi @Dee and Barry Smith
You can try opening the remote and cleaning the circuit board using isopropyl alcohol 99%+ (available from electronics parts stores) or even a clean lint free cloth, where the Power button makes contact with it and see if that solves the problem. There are videos on YouTube that show how to open and clean remote controls.
If the Power button’s conductive contact surface has been worn away through use, then this will be harder to fix. I’ve had some success (about 80%) at repairing remotes with worn out buttons by applying a very small dab of [https://core-electronics.com.au/bare-conductive-electric-paint-pen-10ml.html|electric paint] to the contact surface of the button and then tattooing it into the contact surface using a small pin and then allowing 24+ hours for it to completely dry before reassembly and testing.
When applying just a smear of the paint to the contact surface I found that it didn’t adhere properly to the surface (which is some type of plastic or silicon) and it then fell off as a blob within a few days. By tattooing it in it seems to get a hold into the contact surface material. Do not apply too much though. A little bit goes a long way.
The alternative to to buy a replacement remote for the TV or a universal remote although sometimes depending on the type of universal remote you might not get all the functions that the original remote provided with the TV. Just something to look out for.