remember to call me Bob

Got it, Bob! How can I help you with your compass module today?

what does @D1 do?

D1 is a Texas Instruments TPD4E05U06DQAR, a 4‑channel, ultra‑low‑capacitance TVS/ESD protection diode array for high‑speed signal lines. According to the datasheet, it is a “unidirectional… ESD protection diode” intended to protect interfaces like USB by shunting ESD surges to ground (recommended placement: “as close to the connector as possible”). Its reverse standoff voltage is 5.5 V.

In your schematic, D1 is specifically protecting the USB D+ signal:

So, D1’s role is to clamp ESD events on the USB D+ line to ground, preventing those transients from reaching the MCU/display driver.