unwritable mountpoint

mkdir /tmp/test_dir
chattr +i /tmp/test_dir
touch /tmp/test_dir/test_file # touch: cannot touch '/tmp/test_dir/test_file': Operation not permitted
mount $SOMETHING /tmp/test_dir/test_file
touch /tmp/test_dir/test_file
ls -lah /tmp/test_dir/test_file # -rw-r--r-- 1 root root 8,6K 2024.07.23_21:55 /tmp/123.txt