Screen flickering at the bottom portion of my screen with horizontal lines

One last thing you can try is to run the Apple Diagnostics to see if it uncovers any hardware issues with your notebook. Per chance, did your notebook experience any type of liquid spill?

Ref:

• Use Apple Diagnostics to test your Mac - Apple Support
• Apple Diagnostics: Reference Codes - Apple Support

Hmm. Well everything you have been telling indicates that this may be a hardware issue ... with one or more of the following areas:

• The display itself.
• The cable between the logic board and the display.
• The logic board /GPU

As far as Apple Diagnostics, do you happen to have a monitor available? If so, you can try connecting your Mac to it, and then, run the tests.

Otherwise, since this is getting worse, your best course of action is to contact Apple Support directly. To do so, simply select the Get Support link in the upper right-hand side of this forum's web page. Good luck!

If your notebook displays properly on the external monitor, then that rules out a logic board /GPU issue ... but that still leaves either the display cable, or the display itself, potentially being the issue. Both of these would require an Apple Technician to have them looked at.