If you have set your Facebook profile picture to "Public", anyone on Facebook, even people who are not your friends, can view and download your profile picture. This is because Facebook's default privacy settings allow your profile picture and cover photo to be publicly visible. However, if you change your profile picture privacy settings to "Friends" or "Only Me", then only your Facebook friends or yourself will be able to view and download your profile picture.
If you want to restrict who can see and download your profile picture on Facebook, you can follow these steps:
Go to your Facebook profile and hover over your profile picture.
Click on the "Edit Profile Picture" button that appears.
Click on the "Edit Privacy" button.
Choose the privacy setting you want for your profile picture. You can select "Public", "Friends", "Only Me", or a custom privacy setting.
Keep in mind that even if you set your profile picture privacy to "Friends" or "Only Me", people may still be able to view and download your profile picture through other means, such as by taking a screenshot or by downloading it from a mutual friend's profile. It's important to use a profile picture that you are comfortable with being public, and to regularly review and update your Facebook privacy settings to ensure that you are sharing only what you want to share.