A common problem with refurbished iPhones is the non genuine screen warning which appears on the iPhone 11 and above when a replacement screen is fitted by anyone apart from Apple.
If a screen is not genuine or has been replaced by a third party the Important Display Message appears on the lock screen for four days and in Settings for 15 days.
After 15 days the message remains visible in the about page in the settings menu. This message states Apple was "unable to verify this iPhone has a genuine Apple display" with a link to learn more.
Just like with the Apple non genuine battery warning it is nothing to be concerned about providing the screen has been replaced with a high quality aftermarket part and it will work and perform just as the original did.
When looking for a screen repair or buying a refurbished phone we recommend researching the company first to ensure they have a good reputation and will be using OEM parts which will function just like the original.