I find that saving the data to Excel, then copy-pasting from Excel to Word, generally works much better than directly pasting to Word. I end up doing this a lot, so I wrote a function to quickly open a data.frame in Excel:
# Saves dataframe as .csv in R temp directory, then opens in Excel (or other 
# system default for .csv). The .csv  will have a randomly-generated name 
# unless otherwise specified in `name`.
in_excel <- function (df, name, na = "") {
  csv_dir <- file.path(tempdir(), "csv")
  if (!dir.exists(csv_dir)) {
    dir.create(csv_dir)
  }
  if (missing(name)) {
    csv_path <- tempfile(tmpdir = csv_dir, fileext = ".csv")
  } else {
    csv_path <- file.path(csv_dir, paste0(name, ".csv"))
  }
  if (requireNamespace("readr", quietly = TRUE)) {
    readr::write_excel_csv(df, csv_path, na = na)
  } else {
    write.csv(df, csv_path, na = na)
  }
  shell.exec(csv_path)
}
I'm not familiar with jmv, but per the docs, descriptives returns a "results" object that can be converted to a data.frame:
out <- descriptives(data, 
         vars = vars(Mean1, Mean2, Mean3, Mean4),
         sd = TRUE,
         hist = TRUE)
in_excel(as.data.frame(out$descriptives))