Hank here from Shopify.
As this is account specific, I will just need to verify your account. I will send you an email to the email address attached to this forum's account and confirm some security questions about your store.
Once you reply to that email, I will look into this further for you.
That sounds like it may be a localized issue like your browser, or your Internet service provider (ISP), for instance. Can you try to do this action using incognito mode to see if you are allowed to change the setting? Or even on a mobile device using mobile data if possible instead of your wifi?
If it works on the incognito window, I would recommend clearing your cache to see if this resolves your issue!