@lds333 If you move the entire Sims 4 user folder to the external drive, the Mods folder needs to be inside it just as it would be if you hadn't moved the folder. I didn't read the entire reddit post—it's a little long—but I got the sense that it was saying you could move the Mods folder anywhere IF you were only moving the Mods folder itself, not the entire Sims 4 folder. If you were to move the Mods folder elsewhere, as in, not inside the Sims 4 folder (wherever you put that), the game wouldn't be able to find it.
If you want to double-check your work, this guide is very thorough:
