Why did it stop working and how do I have it fixed ?

My Face ID suddenly stopped working several months ago after a software backup and I didn’t have the fyi about one of the past updates being a common issue meanwhile I had no idea and have updated to the newest update hoping it will fix but I have tried every I’ve seen on YouTube and it tells me TrueDepth camera yet it isn’t because I did that turnt the light downs holding flashlight top of phone with the true depth turning up as i am holding the light checking but having to use pin every time has been very inconvenient for cost of phone that a main feature suddenly stops having to not know what to do for past several months and updates