The description of the encode thoughts cantrip says (GGtR, p. 47; emphasis mine):
Putting a finger to your head, you pull a memory, an idea, or a message from your mind and transform it into a tangible string of glowing energy called a thought strand, which persists for the duration or until you cast this spell again. [...]
If you cast this spell while concentrating on a spell or an ability that allows you to read or manipulate the thoughts of others (such as detect thoughts or modify memory), you can transform the thoughts or memories you read, rather than your own, into a thought strand. [...]
Casting this spell while holding a thought strand allows you to instantly receive whatever memory, idea, or message the thought strand contains. [...]
It also could be more reasonable in scope of power for encode thoughts to simply render a copy of the thought, though this doesn't seem to be what the spell says it does.
Does encode thoughts remove the targeted thought from the creature's memory, or does it create a copy of that thought?
Related and inspired by: Can a creature with a Mind Blank spell active on itself target itself with Encode Thoughts?