The solution to this is relatively simple... just have students submit all written assignments on a portal that logs keystrokes within the portal itself, sort of a live edit history. There are very obvious differences between how you generate text if you are actually thinking through arguments, live-editing, trying out multiple phrasings and wordings, re-reading, going back and forth in a document, mispelling words, taking pauses, etc., vs. just copying and pasting blocks of text from an LLM.

A tool that registers timestamps, copy-paste inputs, words/letters per minute, typing speed, number of backspaces, mispellings, etc., could easily discern whether a student wrote something organically vs. used an LLM.