Sadly, none of the Avengers attended his funeral in Black Panther 2. After his appearance in Captain America 3, T'Challa became a key member of the Avengers, known as Black Panther. T'Challa also opened the door to Wakanda in his own film. One of the most important battle locations even in Avengers 3 is Wakanda. In "Avengers 4", Black Panther is also the first hero to come out of the portal.
However, after such an important character really died, not a single Avenger appeared at T'Challa's funeral. Audiences also expected them to be in attendance, considering that the likes of Bucky Barnes, , Sam Wilson, , the Hulk and Hawkeye were all inextricably linked to Wakanda. In the funeral of Leopard 2, there are only members of Wakanda. Of course, not to mention the production cost of Marvel (after all, so many actors have to be hired back), perhaps because T'Challa's family, in order to protect the cultural significance of Wakanda, only allowed Wakanda people to attend the funeral. Perhaps no one outside Wakanda was told until after the funeral.
In addition to this factor, in "Black Panther 2" some Avengers members, there is no way to attend T'Challa's funeral, such as Thor, Valkyrie, Doctor Strange and Scarlet Witch . In Marvel Phase 4, they are busy with their own adventures. Spider-Man is rebuilding his own life. It is worth mentioning that the director of "Captain America 4" stated that when entering this film, the Avengers had been disbanded. It can be said that although the Avengers is a team, judging from the death of T'Challa, the relationship between each superhero is not so close.
Of course, as far as the Black Panther 2 story goes, while the rest of the Avengers didn't come to T'Challa's funeral, skipping those characters makes more sense for Black Panther 2. "Black Panther 2" isn't a regular Marvel movie -- it's a tribute to Chadwick Boseman and a love letter to his legacy as T'Challa. The presence of any inconsequential characters distracts the audience from the main story and reminds viewers of the myriad of different events that took place outside of Wakanda.
Also, this raises the question of why there isn't an Avenger available to help Wakanda against Namor. By keeping the story intact, Black Panther 2 was only able to focus on T'Challa's impact on his family and home. There is no doubt that "Black Panther 2" as the finale of the fourth phase of the Marvel Universe, at least the word of mouth did not disappoint. The film has been rated very well by critics and audiences alike on Rotten Tomatoes. It can be said that "Black Panther 2" has at least rekindled confidence in Marvel for those who questioned Marvel's fourth phase.