A Lottie alternative for Flutter is usually a change in what the file can do, not just a change in file format. Lottie files are vector animations exported from After Effects. The Flutter Lottie package plays them well, and you can control speed, progress and looping from Dart. What you cannot do is open the file and change its behaviour without going back to the animation tool.
Rive is the closest established option for interactive vector animation. You build the artwork and a state machine in the Rive editor, then drive it from the Flutter runtime with inputs. Teams already using Rive for web or mobile can reuse the same file. The trade-off is cost and lock-in: Rive's free plan exports files that play a Rive splash screen, and paid plans remove it.
ExodeUI takes a similar runtime approach but focuses on product UI. You design states, transitions, springs and events in a visual editor, then play the result through the Flutter runtime. The source is one open .exode JSON file, and the same file can target React, Vue, Svelte, Angular, Solid, React Native, SwiftUI and Flutter. ExodeUI is newer than Rive, so check that the Flutter runtime covers the platforms you ship.
If the motion is a loading spinner, an icon transition or a simple page change, Flutter's built-in AnimationController and implicit animations are often enough. Adding an authored asset only makes sense when a designer needs to control the timing, or when the same animation must appear on several platforms.
Before choosing, test one real screen. Check runtime support for your Flutter targets, how inputs are wired, what happens when the asset fails to load, and whether the tool's licence fits commercial use. A short prototype will tell you more than a feature table.