Please note that init_score is not saved in binary file.
If you need it, please set it again after loading Dataset.
lgb.Dataset.save(dataset, fname)the dataset you passed in
# \donttest{
data(agaricus.train, package = "lightgbm")
train <- agaricus.train
dtrain <- lgb.Dataset(train$data, label = train$label)
lgb.Dataset.save(dtrain, tempfile(fileext = ".bin"))
#> [LightGBM] [Info] Saving data to binary file /tmp/RtmpViPAUB/file13c59f2fec4.bin
# }