If the official website no longer lists firmware (older models are sometimes removed), contact TCL support directly. Provide your (found on the back sticker or in Settings > About). They can email you a direct download link for the correct upd file.
Before downloading any file, it is critical to understand TCL's firmware terminology. firmware tcl 50ep660 upd
Standard system updates via the TV menu often lag behind the latest releases found on community Telegram groups or XDA forums. Updating manually can provide: If the official website no longer lists firmware