Reduce filename sanitization when `--no-windows-filenames` is given

README.md

@@ -609,8 +609,7 @@ If you fork the project on GitHub, you can run your fork's [build workflow](.git
     --no-restrict-filenames         Allow Unicode characters, "&" and spaces in
                                     filenames (default)
     --windows-filenames             Force filenames to be Windows-compatible
-    --no-windows-filenames          Make filenames Windows-compatible only if
-                                    using Windows (default)
+    --no-windows-filenames          Sanitize filenames only minimally
     --trim-filenames LENGTH         Limit the filename length (excluding
                                     extension) to the specified number of
                                     characters

yt_dlp/YoutubeDL.py

@@ -254,7 +254,9 @@ class YoutubeDL:
     outtmpl_na_placeholder: Placeholder for unavailable meta fields.
     restrictfilenames: Do not allow "&" and spaces in file names
     trim_file_name:    Limit length of filename (extension excluded)
-    windowsfilenames:  Force the filenames to be windows compatible
+    windowsfilenames:  True: Force filenames to be Windows compatible
+                       False: Sanitize filenames only minimally
+                       This option has no effect when running on Windows
     ignoreerrors:      Do not stop on download/postprocessing errors.
                        Can be 'only_download' to ignore only download errors.
                        Default is 'only_download' for CLI, but False for API
@@ -1175,8 +1177,7 @@ class YoutubeDL:
 
     def prepare_outtmpl(self, outtmpl, info_dict, sanitize=False):
         """ Make the outtmpl and info_dict suitable for substitution: ydl.escape_outtmpl(outtmpl) % info_dict
-        @param sanitize    Whether to sanitize the output as a filename.
-                           For backward compatibility, a function can also be passed
+        @param sanitize    Whether to sanitize the output as a filename
         """
 
         info_dict.setdefault('epoch', int(time.time()))  # keep epoch consistent once set
@@ -1292,14 +1293,23 @@ class YoutubeDL:
 
         na = self.params.get('outtmpl_na_placeholder', 'NA')
 
-        def filename_sanitizer(key, value, restricted=self.params.get('restrictfilenames')):
+        def filename_sanitizer(key, value, restricted):
             return sanitize_filename(str(value), restricted=restricted, is_id=(
                 bool(re.search(r'(^|[_.])id(\.|$)', key))
                 if 'filename-sanitization' in self.params['compat_opts']
                 else NO_DEFAULT))
 
-        sanitizer = sanitize if callable(sanitize) else filename_sanitizer
-        sanitize = bool(sanitize)
+        if callable(sanitize):
+            self.deprecation_warning('Passing a callable "sanitize" to YoutubeDL.prepare_outtmpl is deprecated')
+        elif not sanitize:
+            pass
+        elif (sys.platform != 'win32' and not self.params.get('restrictfilenames')
+                and self.params.get('windowsfilenames') is False):
+            def sanitize(key, value):
+                return value.replace('/', '\u29F8').replace('\0', '')
+        else:
+            def sanitize(key, value):
+                return filename_sanitizer(key, value, restricted=self.params.get('restrictfilenames'))
 
         def _dumpjson_default(obj):
             if isinstance(obj, (set, LazyList)):
@@ -1382,13 +1392,13 @@ class YoutubeDL:
 
             if sanitize:
                 # If value is an object, sanitize might convert it to a string
-                # So we convert it to repr first
+                # So we manually convert it before sanitizing
                 if fmt[-1] == 'r':
                     value, fmt = repr(value), str_fmt
                 elif fmt[-1] == 'a':
                     value, fmt = ascii(value), str_fmt
                 if fmt[-1] in 'csra':
-                    value = sanitizer(last_field, value)
+                    value = sanitize(last_field, value)
 
             key = '%s\0%s' % (key.replace('%', '%\0'), outer_mobj.group('format'))
             TMPL_DICT[key] = value

yt_dlp/options.py

@@ -1348,12 +1348,12 @@ def create_parser():
         help='Allow Unicode characters, "&" and spaces in filenames (default)')
     filesystem.add_option(
         '--windows-filenames',
-        action='store_true', dest='windowsfilenames', default=False,
+        action='store_true', dest='windowsfilenames', default=None,
         help='Force filenames to be Windows-compatible')
     filesystem.add_option(
         '--no-windows-filenames',
         action='store_false', dest='windowsfilenames',
-        help='Make filenames Windows-compatible only if using Windows (default)')
+        help='Sanitize filenames only minimally')
     filesystem.add_option(
         '--trim-filenames', '--trim-file-names', metavar='LENGTH',
         dest='trim_file_name', default=0, type=int,