According to this recent study: https://youtu.be/Fa7V_OOu6B8?si=p0_fvQyO_G5J-uPJ , (see the 10 minute mark), black bars used with an OLED TV caused burn in after only 700 hours of use. Should I be worried that the same is going to happen with the SteamDeck OLED using EmuDeck given that all the emulators use bars of some sort?
There is no real risk of burn-in unless you are intentionally doing something to cause burn-in like leaving the device on static images for hundreds of hours without changing the image/turning the device off. If you use it like a normal person you will never have any issues.