doc: add descriptions about when options.mode is ignored

PR-URL: #39881
Fixes: #39859
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

doc/api/fs.md

@@ -664,6 +664,9 @@ exist. `data` can be a string or a {Buffer}.
 
 If `options` is a string, then it specifies the `encoding`.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 The `path` may be specified as a {FileHandle} that has been opened
 for appending (using `fsPromises.open()`).
 
@@ -1379,6 +1382,9 @@ The `encoding` option is ignored if `data` is a buffer.
 
 If `options` is a string, then it specifies the encoding.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 Any specified {FileHandle} has to support writing.
 
 It is unsafe to use `fsPromises.writeFile()` multiple times on the same file
@@ -1645,6 +1651,9 @@ changes:
 Asynchronously append data to a file, creating the file if it does not yet
 exist. `data` can be a string or a {Buffer}.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 ```mjs
 import { appendFile } from 'fs';
 
@@ -4086,6 +4095,9 @@ a file descriptor.
 
 The `encoding` option is ignored if `data` is a buffer.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 If `data` is a plain object, it must have an own (not inherited) `toString`
 function property.
 
@@ -4260,6 +4272,9 @@ changes:
 Synchronously append data to a file, creating the file if it does not yet
 exist. `data` can be a string or a {Buffer}.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 ```mjs
 import { appendFileSync } from 'fs';
 
@@ -5216,6 +5231,9 @@ Returns `undefined`.
 If `data` is a plain object, it must have an own (not inherited) `toString`
 function property.
 
+The `mode` option only affects the newly created file. See [`fs.open()`][]
+for more details.
+
 For detailed information, see the documentation of the asynchronous version of
 this API: [`fs.writeFile()`][].