In general, the NBA is in a very healthy space. The game is very popular with younger fans, expanding internationally better than arguably any other sport in the world, and the league will remain highly successful for the foreseeable future.
Discussion about TV ratings and increases in rights fees is tricky because you really have to have a certain level of knowledge about the TV industry to understand what is a positive and what is a negative, and too often people see a figure or a trend and assume it's automatically very good or very bad.
TV ratings across the board are almost always in perpetual decline; the exception being the NFL this season, which is up from the previous year. The NBA being in decline year-over-year is not that big of an issue, unless it is declining significantly compared to other cable and network programs. Viewership that would be considered disastrous ten years okay could quantify as good today. The NBA is still a very healthy television product, it has the youngest average audience than any other major American sport (which is key when it comes the key advertising demo, which correlates more with the value of the program to advertisers than raw viewership totals) and also is arguably the most advanced league when it comes to digital platforms.
At the same time, you also can't necessarily look at increasing television rights and assume that indicates a positive trend for overall popularity. It's certainly a positive for the league's bottom line; but the issue is that the TV industry is currently in a massive race to secure content. Everyone wants to land content people will want to watch, either to save their declining cable/network entities, or to force viewers to subscribe and watch their chosen streaming platform. Sports is seen as a greater premium than anything else, especially to cable/network stations, since it is viewed as more DVR-proof than scripted TV as there is a major factor that makes people want to see it live. Sports also offers a level of security, the tradition of watching sports is ingrained in a huge segment of the population and they will continue to watch their chosen sports regardless of true quality. Because of that, a product can be declining in all measurements (TV viewership, live attendance, digital engagement, etc.) and still see a healthy increase in media rights.
With all that being said, I think the NBA's two biggest challenges are:
1. Rapid player movement, which damages the cultural identity of the league as it prevents certain teams from sticking together for long periods of time. Every year it seems there is a new super team sprouting up, and it's conventional to believe the very best players will easily play for 4-5 teams throughout their careers. I think this hurts teams more at the local level than the national level. At the national level, networks likely don't care that much about which teams are good as long as there are some good ones, but at the local level, it's harder for fans to grow an attachment to a particular team if the players continue to shuffle around each season. A star can be here today and gone tomorrow, and even if they don't leave right away, there is usually a length of drama where a star wants out, or requests a trade, or almost leaves but then stays but it's also only a matter of time until they leave for good. It's a bad environment for creating new fans at the local level, and I think that is reflected by younger fans becoming more frequently fans of individual players and less of teams, although I have no data beyond anecdotal experience to prove that.
I think a related issue is a prospective imaging problem the league will have as more and more players become less patient with their current situation. So much of the league is now about player drama, with players being unhappy and wanting to leave to another market. It sucks up media time and attention as everyone breathlessly discusses how a millionaire in their 20s is unhappy because their team didn't win the title that year and wants to leave. There seems almost like a lack of accountability for top players today; if they bomb out of the playoffs they can just look to change their surroundings, typically at a high cost to their original team. That again creates a negative atmosphere for fans at the local level, even if at the national level its intriguing to figure out where a star player is going to go. LeBron really brought this type of attitude and movement to the forefront of the NBA and other players have taken from his approach to the game and franchise building. The distinction there is that LeBron is the extraordinary rare player who can almost single-handily lead a team to title contention with very little assistance. Only 2-3 players in the NBA are really capable of that in a given time; everyone else is looking to just have a role in the production. It's harder to embellish the antics of Ben Simmons, Kyrie Irving or Paul George, who are All-Stars but not the kind of impactful superstars that lead teams to championships.
2. Stylistic similarity. From an aesthetic standpoint the game has some issues, and the main one to me is that every team plays relatively the same style of basketball. This is heavily influenced by analytics and pretty much every team understanding the most efficient way to play, which can stunt tactical creativity and encourage sameness. So many games now seem to hinge less on individual talent or team execution, and more on whoever happens to have a good shooting night from three, as every team has optimized three point shooting as the critical component to success. I'm not sure what the league will be able to do to change this; in a world where analytics are all publicly available, teams will continue to copy each other to try and gain an advantage. Baseball is dealing with a similar issue; where aspects of the game like the stolen base have been nullified because analytics tell us that it's actually not a great idea to run so much.