You're talking about a notification toast or toast messages (simply). Find the app showing that toast and stop it. You may either disable it, if it is a system app which is more likely as it persists even after a factory reset. However, some OEMs allow preloaded apps can be uninstalled as well which is a godsend for to help remove bloatware or preloaded apps like Prime Video, Netflix, etc. Just figure out which package is showing that toast message on your screen. Force Stopping it will only temporarily fix the problem and it will show the same message again if that same toast is requested or called by the app. It is likely due to a corrupted app or app update, might even be a bugged software update or firmware issue.
Check the internet if other people who own the same model have the same issues or not.
What app is it? If it's one of the YouTube variants it'll be a setting called "stats for nerds" probably hidden behind a 3 dot menu
Do you have an 'Info' button on your remote? I did and whenever I used it on netflix it showed me the quality of the stream, network bandwidth etc in a similar way so might be that it's for displaying some technical information
Did you turn on anything in developer settings?
There is a service/secret menu with a setting that enables that annoying message in TCL/RCA (and some other) tvs. Happened to me one time.
Multiple people asked how to disable this before on the sub.