On the timeline, tap the plus on today's date and choose Calm. The Calm editor opens, titled Calm for today, with two cards stacked vertically — one for Meditation, one for Breathwork. Both start empty, each with a + on the right.
Calm lives on today's date. If you already created a Calm entry earlier in the day, the same editor opens in edit mode so you can add another session to it.
Per-day plus menu showing the Calm option