Well, it depends on what is meant by “average.” There could, maybe within our lifetime after an earth shattering reprioritization of climate change mitigation brought on by widespread death, potentially be another year which is colder than the average of the preceding ten years. Maybe. I won’t say that is impossible although I consider it unlikely.
But there will never again, on any human timescale, be a year that is colder than any “average” as in like the average temperature for the planet starting in the year 1900 or something, or even the year 2000 when it was already measurably above a long term normal level. I am confident that with any level of action on any timeframe that is within the realm of possibility, we will never again see a year that is “average” by that kind of definition.