before

List<String> datas;
final tags = record['tags'];
  if (tags != null) {
     datas = tags;
  }

console

E/flutter (32539): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception:
type 'List<dynamic>' is not a subtype of type 'List<String>'

solution

List<String> datas;
final tags = record['tags']?.cast<String>() ;
  if (tags != null) {
     datas = tags;
  }