The "dark blue light" is the backlight activating with no image data being received by the screen (so black). It is hard to know for sure because of photo conditions and etc., but that looks very bright for "backlight on, screen off", so I'm assuming full brightness on the backlight. Which is default if it receives no other signal. (During boot-up process, the Apple logo at the beginning is always full brightness and the rest of the black screen does look dark blue in some lighting.) Meaning if you do not normally have your brightness maxed out, it is likely not receiving any signal to the backlight either, only power.
If you have tried another known good screen, and got identical results, the most likely answer is your logic board has some kind of damage or possibly broken off components that are critical somewhere in the "processing image for display" to "sending that image to the screen" pipeline. That requires logic board microsoldering repairs. Very delicate and difficult, skilled work that is usually beyond our ability to advise in this forum. There are dedicated repair specialists that do this work, but depending on where you are located in the world it could be unavailable in your area and/or impractically expensive. I know in my area (Alaska, USA) there are no centers within about 1500 miles/2500 km, and sending it off to get a repair of this type usually starts at about $300 USD.
When did this happen? Did it happen when you did a repair of some kind, or after you dropped it or otherwise physically damaged it? Or did it just happen like you went to bed one night and when you checked it in the morning it was like this?
Does the touch function still work? As much as I hate to recommend landfilling a device, the most cost effective way for you to proceed might just be to backup your data (assuming touch function still works, you could likely connect to your computer, look up a tutorial on YouTube to see where the "allow" button is on your phone, and allow the computer to have access to your phone, from which you can use iTunes to facilitate a backup and save your data). This would allow you to move the data to another device at the very least.
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Sounds like your display might be damaged or any light-related issues.
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