Yes, you can modify this using the config attribute:
app = Flask(__name__)
app.config['JSON_SORT_KEYS'] = False
However, note that this is warned against explicitly in the documentation:
By default Flask will serialize JSON objects in a way that the keys
are ordered. This is done in order to ensure that independent of the
hash seed of the dictionary the return value will be consistent to not
trash external HTTP caches. You can override the default behavior by
changing this variable. This is not recommended but might give you a
performance improvement on the cost of cacheability.