What is the blue & gray lines that appear on the lower bottom right of my iPhkne 8 Plus when I reboot it?

SOURCE: Lines on tv screen

Both sound like bad LCD panels. The following must be answered to confirm this:
Do the lines appear on all inputs/all signal sources?
Can they be seen in the OSD/menu?
If yes to both questions, it is likely that the LCD panel is bad

SOURCE: screen appears blue

It's the Light Engine (also called an Optical block) -very expensive.

SOURCE: blue line down right hand side of screen

If you are confident enough to open screen bezel and take out screen , then the second strap from right of your screen has a bad connection. theses cannot be repaired but as a tempory measure some duct tape across the connections will cure it, else replace the screen.

SOURCE: A blue line , 2mm, appearing at bottom of page.

Hi Info39684,
It sounds like your Cyan imaging unit has gone down.
Have you thought of changing the orientation of your paper from A4 protrait to A4 landscape. If the blue line is at the bottom, changing the orientation should hide the problem. It's not going to fix it, and if you use A3 then you will see the line again. It's just an idea and you could save yourself £250 on a new unit.
Regards
Taminol

SOURCE: my sony lcdtv kdf-55wf655 has a blue line across

Your screen has probably been bumped by something.
The line may be possible to be fixed by an engineer reseating the cables internally, but the patchy area is a pressure fault and cannot be fixed without replacing the complete screen.
You can get these patches on things like laptop screens too, where somebody has pressed a finger on them a bit to hard.