dictionary = {'candles': [{
    'open': 78.21,
    'high': 78.28,
    'low': 78.12,
    'close': 78.2,
    'volume': 16417,
    'datetime': 1620385200000,
    }, {
    'open': 78.19,
    'high': 78.26,
    'low': 78.17,
    'close': 78.2,
    'volume': 5928,
    'datetime': 1620387000000,
}]}
res = [val for l in dictionary.values() for d in l for val in d.values()]
print(res)