Man pages matching name bson_decimal128_from_string_w_len in section 3:

bson_decimal128_from_string_w_len.3.en	debian 10 / libbson-doc
bson_decimal128_from_string_w_len.3.en	debian 11 / libbson-doc
bson_decimal128_from_string_w_len.3.en	debian 12 / libbson-doc