The simple way to fix it:(although this may make new bugs)
if (!mounted) return;
This video explaining why you need to fix it (6 minutes) use_build_context_synchronously
The TLDR for that video is that context may not be valid after the async call. The user may have moved on from this UI and now it is out of context.
But what happens if you don’t fix it? That’s the hard to test and answer question. The real answer, and why you are getting the lint is that no one knows. The context may not be valid so whatever the code tries to do may not work and the consequences of it not working may not be obvious.
You will need to see what the code does and what it is using context for and then decide what should happen if the context is no longer valid. The mounted check above will let you know if the context is valid still.