As I'm writing this, I know this is going to be an unpopular opinion for some, but, for me, having watched all five seasons of Star Trek: Discovery, a follow-up movie makes sense. Discovery was cancelled abruptly, which left the team scrambling to film a coda which tied things together a little too neatly. There was a lot of space left between the actual ending of "Life, Itself," the final episode and the ending that was added.
In every other Star Trek series, with the exception of Star Trek: Prodigy, the cast knew the series was ending or was being cancelled. That gave the teams time to properly prepare a series ending. No, that didn't happen with Star Trek: The Original Series, but the cast knew the show wasn't being renewed as the ratings had tanked, and the show had been struggling. And The Original Series ended up with six follow-up movies that gave us the proper ending. And sure, the finale of Star Trek: Enterprise left a lot to be desire, but, again, the cast knew the series was cancelled.
Star Trek: Prodigy was abruptly cancelled after season one, but season two found a home at Netflix, and if the streaming channel doesn't renew it, that second season could properly serve as a series finale. Kevin and Dan Hageman, the creators of Prodigy, planned that.
Discovery got a "finale" of sorts, but it wasn't an ending where the crew knew it was their final time together aboard Discovery. Yes, we know what happened with Saru, and Captain Burnham went on to become an admiral. As for the rest of the crew, we learned that Tilly was still teaching at the Academy at the end of the series, and we know her character will be recurring in Starfleet Academy.
But Discovery had so many other characters that didn't get their finale. And with every other series from Star Trek getting to end things on a final note, it seems only fair that Discovery would get the same treatment, even if it's a streaming channel movie. Those of us who enjoyed watching this series want to see the crew know their time together is coming to an end. We want to hear the goodbyes and know what happens to everyone as they go on to live their lives without Discovery.