The Sims 4 has the friendliest cheat system of any game in this database, and the most common complaint about it — "the code did nothing" — almost always comes down to one missing step.
Opening the console
Press Ctrl + Shift + C on PC, or Cmd + Shift + C on Mac. A text box appears at the top of the screen. On console, hold all four shoulder buttons at once.
The step everyone skips
Type testingcheats true and press Enter, before anything else.
Most Sims 4 cheats are disabled until this is on. Enter a money cheat without it and nothing happens — no error, no message, just nothing. That silence is what sends people looking for a different code when the code was never the problem.
It resets when you quit, so it must be re-entered each session.
Money
motherlode — 50,000 Simoleons.kaching — 1,000 Simoleons. Useful when you want a nudge rather than a fortune.
freerealestate on — makes every lot free. This one only works from the world-selection screen, not while you are on a lot, which is another common source of "it did not work".
Building and creating
bb.moveobjects — removes placement restrictions so objects can overlap and sit where the game would normally refuse. The single most useful build cheat there is.
cas.fulleditmode — unlocks full Create-A-Sim editing for an existing Sim, including traits and age. After entering it, shift-click the Sim and choose Modify in CAS.
What cheats cost you
The Sims 4 has no achievement penalty for cheating, which is unusual. Nothing is locked off and no progress is invalidated. The only real cost is to the game's own difficulty, which is entirely your business.