There is no arrivals lounge at CDG except the AF one in T2 (which I think is a nice terminal). It is one of the downsides of flying UA into CDG at the much worse T1. (Interesting aside: both terminals were designed by the same architect, just decades apart.) When arriving on UA, you will enter the same area that the *A lounge is in, which is before the passport control and the baggage claim on the other side of that, but their policy is not to admit arrivals. (Not to say someone does not slip in from time to time, but I have been turned away.) You could use the SalonICARE lounge near it with PP, but it has no showers (and is always crowded). Same with SAS (which is only for departing and has no showers), and LH (only for departing and with no showers, and also behind the security screening for the little LH outposts that T1 uses).
Also, even if you could get in to the *A lounge on arrival, I would not do it if I had checked luggage, since it is not a good idea to leave your luggage at the T1 baggage claim for very long, and with the automated gates and no ongoing ticket, I don't think they would let you back into the passport controlled area where the lounges are.