use qmk.path.normpath to locate the output file.

lib/python/qmk/cli/json2c.py

@@ -1,7 +1,6 @@
 """Generate a keymap.c from a configurator export.
 """
 import json
-from pathlib import Path
 
 from milc import cli
 
@@ -9,7 +8,7 @@ import qmk.keymap
 import qmk.path
 
 
-@cli.argument('-o', '--output', arg_only=True, type=Path, help='File to write to')
+@cli.argument('-o', '--output', arg_only=True, type=qmk.path.normpath, help='File to write to')
 @cli.argument('-q', '--quiet', arg_only=True, action='store_true', help="Quiet mode, only output error messages")
 @cli.argument('filename', arg_only=True, help='Configurator JSON file')
 @cli.subcommand('Creates a keymap.c from a QMK Configurator export.')