Ninja Kiwi has largely rendered unofficial save editors obsolete for "fun" purposes by integrating official creative tools into the game:
Note: I cannot provide direct links to download pages for modding tools as they often bypass payment systems for in-game currencies. btd6 save editor updated
Use the BTD6 Save Editor to skip grind you’ve already done legitimately, not to ruin leaderboards for others. The update makes it easier to experiment, but a little restraint keeps the game fun for everyone. Ninja Kiwi has largely rendered unofficial save editors