It might not be a simple fix as finding out what is wrong may be involved and require using a DMM (digital multimeter) on the power board where exposed lethal voltage is present
It may be the same problem that is causing both fault conditions or perhaps it may be two separate problems.
I’m not trying to dissuade you from fixing the TV, I’m just trying to explain what might be involved in finding out what’s wrong.
With the black line down the screen, this could either be a TCON board problem, a tab problem or worst case a panel problem.
Check the Tab connections to the LCD panel. These connections are extremely fragile and sometimes they just lift off. Try pressing down gently on the tab connector above where the line appears on the screen to see if it removes the line.
If it does then you may have to contrive a way to make it stay down. Perhaps tape but be gentle.
It may be in the tcon board but this would have to be replaced to see if it were there or not.
If checking the tab connection or replacing the tcon doesn’t fix the problem then it is in the panel, which cannot be repaired. It has to be replaced.
The difficult part with this is finding a replacement panel. Find the panel part number on the back of the panel itself and search online using the part number. You may be lucky. If you do find a replacement you’ll find that it will nearly cost as much as a new TV. An option to consider then if you can’t live with the problem is to advertise the TV as faulty screen - good for parts as TV boards are always in demand, to recoup come of the cost towards a new TV.
With the flickering, try the following to see if is a LED backlight problem (or a power board problem) and not a video signal to the panel problem.
Turn off the TV and disconnect the power cord from the wall outlet. Remove the back cover from the TV and then disconnect the cable that goes between the power board and the mainboard. Reconnect the power cord to the wall outlet and switch on the TV.
The TV LED backlights should come on steady and stay on - no flickering. There will be no picture because the mainboard is disconnected.
If they flicker there may be a problem with the power board or the TV backlights. This is where you will need to use the DMM on a “live” TV to find out where the problem is.
If it is the power board then it is easy to replace. If it is the LED backlights, this will involve dismantling the TV to get access to the lights and then finding and fixing the problem.
If they don’t flicker, then the problem may be in the tcon board, tcon board -mainboard cable (or connections) or the mainboard.