The movie doesn't have to explicitly be about dragons, but dragons need to be featured as more than just a passing comment or minor cameo or scene.
I love the Eborsisk in Willow. It's a very unique two-headed fire breathing dragon that is somehow both incredibly ugly and very cute, and Willow is one of my favorite films.
Rathalos from Monster Hunter and King Ghidorah from Godzilla are also very cool dragons.
Damsel just came out this year. Haven't seen it yet, but the trailers looked good.
The d&d movie, honor amongst thieves has a damn fun dragon scene in it, and it's more than a simple one-off imo. It's borderline though, might not be what you're looking for exactly, but worth watching. There was also an older d&d movie that was built around dragons. As a movie it was kinda meh, but the dragon parts were decent. That's the one that wasn't on the syfy channel. The TV one was meh across the board.
There was eragon, but I've never seen it. A lot of people that were fans of the books hated it, but maybe someone coming to it fresh wouldn't.
Dragonslayer is much older, it came out when I was a kid. So, don't expect great effects by modern standards, but it's an awesome movie.
There's the Hobbit movies. The Dragon, Smaug is central to the story, though not present until the end.
Reign of Fire was pretty damn good at the time, though I don't know how well it holds up. But I still like it enough to watch it now and then.
Oh! And dragonheart! A brilliant movie that absolutely holds up.
Those are the ones I can think of.
Now, I didn't mention any animated ones. That's because I don't really think most of those do Dragons justice, not the ones that meet the featured criteria anyway. Like, Pete's Dragon is awesome, a great movie. It just isn't what I think of as a dragon movie. Same with Spirited Away, which has a dragon as very integral part of the story, but it isn't a dragon movie in the same sense as The Hobbit is.
But, if you want animated options, those two are a great place to start.
Obviously, there's also the game of thrones stuff, but that's series, not movies. Great dragon scenes for sure, and they're integral to both series.
I loved the Themberchaud scenes in Honor Among Thieves! Man, what a wonderful movie in general. I hope it becomes a series.
Eragon was very watchable. It wasn't great, but it was fun enough.
I had all but forgotten about Dragonslayer! I loved Peter MacNicol as Galen in that. It was surprisingly good! I remember seeing this in a double feature with Krull.
I still have not seen the last two Hobbit films, I've only seen the first.
Reign of Fire still holds up, and it had a fairly fun video game adaptation. My only gripe is that it definitely teased a sequel that I doubt we'll ever see.
I absolutely LOVE the first Dragonheart. As for the sequels... there should have only been one Dragonheart.
The Game of Thrones stuff is awesome, and I especially loved Viserion. That may be the only time we've seen a dragon like that on screen.
Great list! Thank you for reminding me of Dragonslayer! I need to watch that again.