Inter still has the upper hand to win the league because Napoli isn't consistent anymore. This is the only challenge that Napoli has. No one can tell if Inter will be strong till the end of the league and if that happens, it means that there's no hope for Napoli because Inter will win their matches.
This season the competition for the trophy is very tight, Inter Milan and Napoli both have the same chance even though Inter is currently 3 points ahead of Napoli. However, the points difference can be caught up by Napoli if Inter loses points in two matches and Napoli takes advantage of the opportunity in the remaining matches to continue to perform consistently. This should not be difficult for Napoli considering that the opponents they will face in the remaining matches do not have tough opponents.
Another advantage for Napoli at this time, they are only focused on Serie A while Inter still has the Champions League and the Italian Cup. With so many matches, Inzaghi must find a strategy and must have an idea in playing players in each match to maintain the stamina of the players so that they do not get tired.
I can't tell of UCL, but based on their last match against Bayern, they have the higher chances of qualifying to the semifinals.
Inter was not favored at the beginning of the UCL like Real Madrid, Barcelona, Liverpool, Arsenal or PSG. However, Inter can progress until now showing that Inter is a strong team, and is still the team with the fewest goals conceded. No need to play beautifully or win by a big score, a one goal difference is enough to win. So it's true, with Inter's current game and Munich's weak defense, I am sure Inter will enter the semifinals and face Barcelona who are certain to qualify.