If you set the argument save_latent_dynamics = TRUE when running variational then there’s a separate CSV file that’s saved that I think contains this info (it’s an experimental feature so not fully documented at the moment):
fit <- mod$variational(..., save_latent_dynamics = TRUE)
fit$latent_dynamics_files() # gives you location of the CSV file
If I remember correctly for variational this extra file has a column of ELBO values.