I found that information now, thanks @muellerzr!
Just an observation for anyone else looking at the same: learn.summary only tells you the number of groups in the model if you run learn.freeze_to(x), learn.summary() where x is >= number of groups (and it’s told as a warning before the tabular output, since it’ll be freezing all groups then).
In case x is less than the number of groups, the only information you get is a
Model frozen up to parameter group number x