It is common for Starship prototypes to have uncontrolled fires, but it is obviously not a good thing.
For example, prototype number 10 exploded 8 minutes after landing [1] because of a seemingly insignificant fire at the bottom.
After today's flight there was a long lasting fire in the engine section, with occasional flaming pieces of plumbing raining down from the rocket. Examining the aftermath should help SpaceX to understand what improvements need to be made to prevent this from happening.
This highlights another thing I love about watching SpaceX's unprecedented rate of progress. They're managing the complex balance of risk, learning, time and budget extremely well. I'm not an expert in the relevant domains but even I've noticed and appreciated that the typical SpaceX development test always manages to get big chunks of new data, while still having some notable things not quite working.
It's an object lesson in rapid engineering development. If everything goes perfectly in a development test, it's a sign you're not moving fast enough (meaning not taking enough risk per increment to maximize learning). As valuable as Falcon, Starlink and Starship are, the biggest near-term value of SpaceX may be providing such a clear demonstration of well-executed "fail fast, learn fast" engineering that even politicians and bureaucrats can understand it.
Maybe the flare on the side started as purposeful. But there was also a fire inside, between the engines, with flaming pieces of some pipes or cables raining down from the rocket. You can see one example of this just after this timestamp: https://youtu.be/YC87WmFN_As?t=12928
For example, prototype number 10 exploded 8 minutes after landing [1] because of a seemingly insignificant fire at the bottom.
After today's flight there was a long lasting fire in the engine section, with occasional flaming pieces of plumbing raining down from the rocket. Examining the aftermath should help SpaceX to understand what improvements need to be made to prevent this from happening.
[1] https://youtu.be/XOQkk3ojNfM?t=38346