21 h layover in CDG - stay near airport or go to Paris downtown?

With a 7 PM arrival from Seville, I think you can make it to central Paris in time for a late dinner (maybe 9 PM), and enjoy Paris for a whole morning before leaving for CDG at around 12:30/1 PM.

That's what I would do.

I’d do as balso suggests. Plenty of time to get a hotel in central Paris and enjoy the evening and morning in the city.

For these types of stops, I always recommend the Henri IV on the rue St. Jacques. It’s just across the river from Notre Dame and a 5-min walk to the RER B, making getting to and from the airport a breeze.

https://henri-paris-hotel.com/en/

3rd vote for Balso's suggestion! I'd definitely stay in Paris....unless the weather is horrible! But still, I'd not want to be stuck at an airport hotel for your whole morning. That will be a Sunday night to Monday departure.

Have you been to Paris before?

Editing to add: Your hotel will generally stash your luggage for you between check out and when you probably should leave for the airport between 12-1230.

Great advice above from all.
Poster 'Happy', you mention the Henri IV. Did you ever stay at the the old zero-star 'hotel' of the same name that used to be in Pl. Dauphin on Ile-de-la-Cite?
It was a dump, the stuff of traveler legend. The wicked manager woman at front desk used to harangue guests foolish enough to make any request of her beyond the handover of keys.
"Whaddya' mean youz needs toilet papers?! CHILDRENS DYING AFRICA AND YOU SAY THEES REQUEST?!"
Hilarious because she was being serious.
I am done. the end

greg, I never stayed there, but the battleax sounds familiar. I wonder if she ever worked at the Hotel Cambon. She yelled at us for turning on the hall light to see us to our room. And refused to give us more soap for the bath. We had to go buy it. This was years and years ago. Funny now, but...

Thanks! Been to Paris 2x (last time I got really, really sick!). I'll look for the hotel.