GNU Radio 3.10.4.0 for Windows
Python

By default IIO attribute source block attribute type register output value is np.float64. To change it to np.float32 modify file iio_attr_source.block.yml. In (radioconda installer) GNU Radio it is located in radioconda\Library\share\gnuradio\grc\blocks directory.

-   id: type
    label: Data Type
    dtype: enum
    default: "'Input'"
    options: ['0', '1', '2', '3', '4']
    option_labels: ['Double', 'Float (casted from double)', 'Long Long', 'Long (casted from long long)', 'Bool']
    option_attributes:
      fcn: [f64, f32, s64, s32, s8]
    hide: ${ ('part' if (attr_type != '3') else 'all') }
=>
-   id: type
    label: Data Type
    dtype: enum
    default: "'Input'"
    options: ['0', '1', '2', '3', '4']
    option_labels: ['Double', 'Float (casted from double)', 'Long Long', 'Long (casted from long long)', 'Bool']
    option_attributes:
      fcn: [f64, f32, s64, s32, s8]
    hide: ${ ('none' if (attr_type != '3') else 'all') }