I arrive CDG on a Tuesday and leave the following Monday. It seems the Navigo weekly pass is a good option through Sunday. So, on Monday what’s the best option to get from central Paris to CDG? Thanks!
Yes, Navigo week pass will be your best option Tuesday thru Sunday.
Then for Monday, if you're looking to do 4 or more one-way Metro trips in central Paris before your trip from Paris to CDG then a Navigo Day Pass (aka Navigo Jour) 1-5 zone would make sense. This will cover unlimited trips both in the city and your trip from central Paris to CDG using either RER B or Roissybus (departs on west side of Opera Garnier), whichever is your preference.
If you're planning on 3 or less Metro trips in central Paris trips on Monday prior to going to CDG, buying single-use paper Metro tickets (2.10€ each) as needed and then a single-use RER ticket for Paris to CDG (same price from anywhere inside Paris, 11.45€ as of 2023) is the cheapest option.
Note that you can buy/add the Navigo Day Pass to your Navigo card at the same time you buy/add the Navigo Week Pass (on Tuesday when you arrive). You can ask the ticket agent to make the Navigo Day Pass active for next Monday. (Navigo Day Passes can be added to a Navigo card up to 6 days in advance of its "active" day.) So you'll have both your Week Pass and Monday Day Pass on the same Navigo card. And the Day Pass will become active the moment your Week Pass expires.