There’s a lot to unpack here, so I’m going to give a general kind of advice that should be helpful for anyone trying to get cleaner video:
There are two main aspect to the image transmission: the camera and the VTX.
Whenever you have noise, the first step would be to increase power filtering as much as possible.
The easiest way to do this is to add a capacitor to the battery pads to filter out the voltage spikes.
If that doesn’t work, try powering your VTX from a BEC on your flight controller instead of VBAT (if that’s what you already have).
Also try powering your camera from a BEC on your VTX if it has one.
Then try adding a common ground between the camera and the VTX to avoid what is called a ground loop.
There are other sources of power noise, which could include oscillations that cause voltage spikes in the motors.
The antenna you use also has a big impact on video.
The best way to ensure good video link quality is to have two circularly polarised antennas with the same polarisation, for example RHCP with RHCP and LHCP with LHCP.
You can also use a patch antenna to increase the reception of your goggles at the expense of the number of directions from which you can receive a signal.
Have you ever powered on your VTX without an antenna? This can sometimes cause the VTX to become damaged.
If you have a spare VTX, try using that and see if quality improves.
If you’re flying in a wide area, you can try increasing your VTX power (as long as it is legal).
If you’re flying in a tight space like a bando, sometimes having a higher power output can actually make the video signal worse due to multipath interference. If you experience that, you may want to try lowering the power output.
Make sure your goggles are on exactly the same frequency as your video transmitter.
People often use the auto-scan function on their goggles, however this is known to be inaccurate and often goes to a close channel, but not the exact one.
The wrong frequency will introduce static, but it is unlikely to create the lines you describe.
It is also possible that lines may be caused by RF interference from WiFi, power lines etc. You may be able to get around this by changing your frequency.