You are right in saying that Chelsea cannot be regarded as the most popular one; with a younger team, which is yet to mature. However, the history tells that they are capable of shocking people and the win over PSG in the Club World Cup definitely provides them with confidence. Their greatest weakness however is their lack of consistency since they are at times unable to maintain their good performances. I believe given the coaching of Maresca and the talent that they possess, Chelsea might very well go deep into the tournament. They are not to be dismissed lightly, though, since as you pointed out they can create some massive upsets.
This season will be very different from last season, so other teams will be taking every opponent in this tournament more seriously. Chelsea has made a resurgence since winning the Conference League and the Club World Cup, so they deserve to be watched by all opponents in this tournament. Last season, everyone saw that Chelsea wasn't very consistent in the Premier League, but they were consistent outside the Premier League, causing a major upset in the Club World Cup. And in the Champions League next season, Chelsea is certainly capable of making even greater breakthroughs.