What's the difference between 逐渐 and 渐渐？

逐渐: emphasize change based on a certain foundation
渐渐: emphasize the natural change of something from nothing

https://www.cchatty.com/grammar/10328

“逐渐”is a little more formal and usually used in written form. “渐渐”is usually used in informal situation.
They have no difference in meaning.
E.g. 1. 一到十一月，天气就渐渐地冷了。（很口语，用“渐渐+地”更合适。）
2. 经过精心调养，他的身体正在逐渐恢复之中。（书面语语境，用“逐渐”更合适）

there is no different.