https://dart.dev/guides/language/effective-dart/usage#avoid-using-curly-braces-in-interpolation-when-not-needed says to avoid using curly braces in interpolation when not needed. If you’re interpolating a simple identifier not immediately followed by more alphanumeric text, the {} should be omitted.
Is there a problem doing it aside from it being not necessary to do interpolation?
The guide says this is good:
'Hi, $name!'
"Wear your wildest $decade's outfit."
'Wear your wildest ${decade}s outfit.'
The guide says this is bad:
'Hi, ${name}!'
"Wear your wildest ${decade}'s outfit."
It is not a problem since $decade are just a shorthand for ${decade}. So both Strings will end up compiling into the same code. The linter rule is about taste and make the code consistent in your code base.
You can see this in Dart Language Specification in the chapter about "String Interpolation": https://dart.dev/guides/language/specifications/DartLangSpec-v2.2.pdf
The form $id is equivalent to the form ${id}.
To customize which linter rules will run, see the following link: https://dart.dev/guides/language/analysis-options