What’s happened to Star Trek is the same thing that’s happened to every iconic franchise. Back then, the people making TNG had a clear vision (well, except season one). They also had limitations, many of them imposed by Gene Roddenberry himself. The writers, producers, and actors had to actually think and be creative, not just slap some CGI lasers on the screen and call it a day.
TNG was filled with stories that dealt with big ideas like AI rights, ethics, diplomacy, philosophy, and the morality of the Prime Directive. The crew behaved like professionals doing their jobs. DS9 was the opposite to TNG. It had drama, conflict and war. But it took its time, building up those themes over four-five seasons and it was still Star Trek.
Modern Trek, on the other hand, is obsessed with revenge, drama and conflict and nothing else - it’s basically The Anti-Star Trek. I honestly doubt the current showrunners even know what the Prime Directive is. Every character acts like a child who wouldn’t survive high school, let alone belong on the bridge of the Federation's flagship!
And I get it - they’re trying to reinvent the franchise for a new audience who’s never seen Trek. But, they’ve only managed to alienate the old fans while failing to bring in new ones. Netflix isn't buying the rights for Discovery or any other new Trek. But they’ve kept TOS, TNG, DS9, Voyager and Enterprise in their library for years...