TDLR: any macbook will be more than enough for simple daily use needs with the basic amount of security. 
That won’t prevent your dad from being phished or installing malware tho, there is also some basic knowledge to have when browsing the Internet. 
But overall, out of the box and without a high threat model, you’re 100% covered with MacOS.
Consider recommending him a good offline password manager maybe + other tools from PG’s recommendations to cover all of his digital needs.
Otherwise, I’ve shared a post about the Neo already where quite a few other discussions happened, feel free to check it here: Macbook Neo
Buying a Neo or any other M chip will realistically not change anything in practice (regarding security) for your father.