Hello Creative Cow! I'm trying to flip a line that I've animated so that it animates going the opposite way. However, nothing I'm doing is having any effect on the animation. I've tried unlinking the X and Y coordinates on the scale option and making X -100, I've tried going to Layer -> Transform -> Flip horizontal. I have absolutely no idea what I'm doing wrong, or what I've done wrong.
If by "UI" then you mean the workspace, then sure lol Here is my UI.
The fourth shape with the menu dropped down is the shape that is supposed to be flipped. As you can see, I have already unlinked the X and Y coordinates, as well as made the X value -100.
Precomposing, as Dave suggested, is an option here, but it's not the one I would choose first. Precomposing is often necessary for technical or organizational reasons, but here, it comes at a price: complexity. Once you precompose, you no longer have access to all the properties of an animation in the same timeline. You have to move between timelines to revise an animation.
The reason that you weren't seeing a change when you tried scaling to [-100,-100] % is because scaling always happens around an anchor point; your anchor point here is the very center of the solid.
To keep these elements in the same comp and also be able to flip them with scaling, add a Null object to the comp. (By default, it will be positioned in the center). Make the Null the parent of the layer 4 solid by dragging the parenting pickwhip icon on layer 4 and selecting the Null layer. Now, you can adjust the scale of the null itself. All the children of the null will transform around the null itself.