The RoissyBus shuttle provides a direct link between Paris (Paris-Opéra in 60 minutes) and Paris-Charles de Gaulle airport.
Journey time: approx. 60 minutes.
Fares (available for 2022): €13.70
You can pay now directly at the driver, with cash or card, and this was a nice surprise, since in the last years you could only use cash to buy a ticket directly from the driver.
You can use the forfait Navigo, zones 1-5 accepted).
Also you can buy a ticket online or from the vending machine you'll find in the Paris - Opera station.

RoissyBus stops at Paris-CDG airport: Terminal 1 - Terminal 3 - Terminal 2AC - Terminal 2D - Terminal 2EF.
RoissyBus stops at Paris: Paris-Opéra (Corner of "rue Scribe" and "rue Auber").

Frequency:

Frequency from Paris (Opéra) - Charles de Gaulle:

5:15 am to 8:00 pm, every 15 minutes
8:00 pm to 10:00 pm, every 20 minutes
10:00 pm to 00:30 am, every 30 minutes

Frequency from Charles de Gaulle - Paris (Opéra):
6:00 am to 8:45 pm, every 15 minutes
8:45 pm to 00:30 am, every 20 minutes