The usual answer, and why it is only a starting point
Once per heating season is the standard guidance for a regularly used wood-burning fireplace or stove, and it is a reasonable default. But the interval that actually matters depends on how much creosote you are producing, which varies enormously between households.
Two homes burning the same volume of wood can produce very different deposits depending on wood moisture, how the appliance is operated and how warm the flue runs.
What accelerates buildup
Unseasoned wood is the biggest single factor, because the energy that should be heating the flue is spent boiling water out of the fuel instead. Smouldering fires and heavily damped overnight burns do the same thing.
An oversized or exterior uninsulated flue also cools gases below the point where they stay in suspension, so deposits form even with good fuel and good technique.
Signs you should not wait
Black flakes in the firebox, a tarry smell on humid days, smoke pushing into the room, or a shiny black glaze visible in the flue all mean the interval has already been exceeded.
Glazed creosote in particular does not wait for next season. It burns hot enough to crack a tile liner, and removing it needs a chemical treatment and a follow-up visit rather than a single sweep.
Gas and pellet appliances are different
Gas appliances do not need sweeping in the wood-burning sense, but they do need an annual service that cleans the burner and pilot and verifies the vent.
Pellet appliances need the most frequent attention of all: user cleaning weekly during the season, plus a full technician service each year.