In order to improve your FPS in Terraria (on mobile phone), you have to copy the following settings.
You will need to set Parallax to 0%.
And turn on the Frame Skip, Set the Lighting Mode to Trippy.
And VFX Quality to Low.
You have to turn off Backgrounds, Blood, & Effects.
And turn all graphics to low.
After that, you should be getting more frames.
For PC, you will need to copy the following settings.
You will need to turn on the Frameskip, And set the Lighting to Retro.
You have to turn off the Background, And also turn off Blood & Gore.
After that, disable Heat Distortion & Storm effects, Also, disable the Heat Distortion & Storm Effects.
Your frames should be much better now.