But I think these are different enough capabilities that the success or failure of one is not necessarily predictive of the other.
Just google news Memojis and see what you get. Hardly any content, and if you navigate 2-3 pages further, you quickly reach 2022 and 2021 articles.
If that doesn't scream "low adoption" then I don't know what does.
Google Trends seems more likely to be instructive, and as a topic, it has shown fairly steady (if low) interest over time after peaking on release with some periodic spikes most likely correlated with major updates.
But as a feature, I wouldn't expect even Google trends to be very instructive (for understanding adoption), since people who know how to use them aren't likely to be out there searching. More use = more familiarity = less searching. Who knows; maybe they're barely used, but there isn't good data to back up that claim, and there are a number of other ways to interpret the data that does exist.
With all of that said, I'll maintain that I don't see any real connection between them and Personas, or any predictive value in comparing them.
For the record, my point here was: More use = more familiarity = better writing subject for portals and journalism
But it’s been over 5 years since Apple started pushing Memojis, they still continued as recently as last year and they have little adoption still, as far as I am aware.
Those who watched WWDC remember how cringey those Memoji bits were, I specifically refer to that aspect of their being increasingly out of touch.