I don't know if there are any matches in the champions league that are less popular, considering that this tournament is one of the most prestigious in Europe and in other continents such as Asia, this match is highly anticipated but it is specifically for big clubs, so I don't know if it is a recording or the original sound of the audience, but I remember very well at the beginning of the pandemic when matches had to be played without spectators, the organizers used recorded sounds but there were also sounds from television broadcasts with the audience being able to choose with or without sound
https://www.nytimes.com/2020/06/16/sports/coronavirus-stadium-fans-crowd-noise.html

and during the pandemic even in tennis matches they used images of spectators to make it look crowded even though there were no spectators in the stadium apart from the organizers.

So it is very possible that it is a recorded sound because the lack of spectators is also said to affect the performance of the match.