ABBA never made a Christmas record. The four did sing a few impromptu Christmas songs, usually on radio broadcasts, and there were a few recorded spoken-word Christmas greetings released on giveaway flexidiscs.
Agnetha recorded a Christmas album with her daughter Linda, 1981’s Nu tändas tusen julejus (Now a thousand Christams candles are lit) . Benny’s pre-ABBA group The Hep Stars recorded an album Jul med Hep Stars (Christmas with Hep Stars) in 1967. Both Frida and Björn’s group Hootenanny Singers recorded songs for a Polar Music Christmas album, När juldagsmorgon glimmar (When Christmas morning shines), in 1972.
ABBA remained away from any songs that could be restricted to any seasonal event, with the one exception ‘Happy New Year’ (on Super Trouper, 1980), which is more a song of wistful reminiscence than a song to be played at midnight on New Year’s Eve (not that that stops many people from actually playing it then).
Personally I’m glad that ABBA never recorded a Christmas album. Most of them are too kitsch, too sugary, and most of them sound the same. Very few have anything to offer artistically. ABBA remained secular, without trying to appeal to a small niche market or disenfranchising any part of their audience.