STRINGdb: reverse map STRING identifiers to gene names?
This answer does not rely on STRINGdb package.
STRING provides supplementary identifier mapping files here: https://string-db.org/mapping_files/.
It looks like you are interested in human STRING name one - https://string-db.org/mapping_files/STRING_display_names/human.name_2_string.tsv.gz. You could read it as a separate lookup.