Q.White lines on succulent plant.
I had this succulent for years and about 2-3 months ago I propagated it because it was growing very tall. I also introduced it to a grow light for about 2-3 months too.
Recently I noticed white lines on the leaf. 1 leaf at the bottom is dryer up with the white lines.
Certified GKH Gardening Expert
That appears to be insect damage. This collection of articles will help you to create pests control methods that you likely already have in your kitchen: https://www.gardeningknowhow.com/special/organic
What kind of light are you using? I see what appears to be a little bit of light damage. This can happen for several reasons. Sometimes with LED's they only contain two spectrums: Red and Blue. This is not enough to sustain happy plant growth. Led's should contain at least 9 bands to sustain good growth.
Sometimes the light can be too close causing damage as well. If you can include photos of your light source, I can help you to determine if light damage is due to the source, or from being in, both, sun and synthetic light at the same time, which will be unnecessary.
If this is a gaslit bulb such as metal halide or high pressure sodium, then the light could be slightly too close.