Prefill hidden field with News-Title or similar data

Use a hidden field with section ValueFromTypoScript. The value field contains a marker name, in which the required Data string is written:

fields {
    objekttitle < plugin.tx_fluidform.presets.fields.hidden
    objekttitle {
        label = Immobilie
        section = ValueFromTypoScript
        value = lib.openimmo.objekttitel
    }
}

The marker can be filled as usual by a TypoScriptRECORD object:

lib.openimmo.objekttitel = COA
lib.openimmo.objekttitel {
    wrap = This is the title:|
    10 = RECORDS
    10 {
        # id des template-records
        source = {GP:tx_openimmo_immobilie|immobilie}
        source.insertData = 1
        tables = tx_openimmo_domain_model_immobilie
        conf.tx_openimmo_domain_model_immobilie >
        conf.tx_openimmo_domain_model_immobilie = TEXT
        conf.tx_openimmo_domain_model_immobilie.field = objekttitel
    }
}