Ron clearly said in his channel that "comma + which" modifier can NEVER modify a preceding noun + modifier, he said in some cases you can use "which" to modify a noun + preposition.
" xxx's letter to susan dickenson, which...", I clearly remember this official question, "which" was used to modifer letter instead of susan dickenson.
" the apple on the chair, which is plump and delicious..." this is fine, as we are modifying the apple + preposition
" the apple on the chair, which was made with wood..." this is also fine, as we are modifying the noun in the preposition
But according to what he said, you can NEVER EVER have something like "the apple that the witch grew" followed by a comma +which that tries to modify the apple; nor can you have"most student who spend time playing video games..." followed by comma + which to modify student.... YES I am absolute on this.