Bus from Gare de Lyon to Charles de Gaulle? Latest bus or RER?

If you take the RER A from Gare de Lyon to Les Halles, it is a simple cross-platform transfer to the RER B to CDG.
What time do you want to leave? The schedule is for the RER B is at https://www.ratp.fr/en/itineraires
I believe the express bus between CDG and Gare de Lyon has been discontinued.

I'm pretty sure that the Air France buses were discontinued around the time
of the pandemic. You do realize you can take RER from CDG to Gare de Lyon
with a change at Chatelet?

You need to look up schedule information directly on the RATP site. Especially
with the Olympics and the fact that you don't say when you want to travel, the
train schedules are likely to be variable for at least a few weeks.

But I am pretty sure that the RER runs into the late hours, and not quite sure
why you would want to head to the airport at midnight?

"Any advice or suggestions that would help me stay in Paris as late as possible would be very welcome!"
The RER does run pretty late and if you want to hang out in Paris later, there is always the Noctilien bus system that operates from around 12:30 AM to 3:30 AM. You can find directions by going to the RATP website and seeking directions for a late night/early AM trip.
And yes, the Air France Bus (Les Cars) service is no longer in existence.

You can always call a cab if you misjudge.

As others have said (just to underline that their information is correct since I have no way to "upvote" their response), the Cars Air France service (the bus you remember between CDG and Gare de Lyon) died with the pandemic.