Core intentionally doesn't invent a special "paper-encryption" scheme or mnemonic. If you want a physical backup you have to add the protection yourself.
Core devs generally recommend encrypting the wallet (encryptwallet), then keep multiple offline copies of the encrypted wallet.dat in different places (USB/offline disk, etc.).
I am not sure about the "intentional" part. Perhaps they've found some ways to do it manually that aren't standardized and that's why they're not featured in Bitcoin Core.
I am not a fan of digital backups. If you have 3 media in which you store your
wallet.dat, chances are you'll be ok, but I prefer trusting paper.
The problem is, that the easiest way I 've found so far for doing a proper backup is the following:
1. Export the private descriptors in a JSON file.
2. GPG-encrypt the json file.
3. Print the encrypted cipher.
The cipher though looks like this:
-----BEGIN PGP MESSAGE-----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=Wqxk
-----END PGP MESSAGE-----
Easy to print, but very difficult to write down in order to decrypt it.
So, getting a QR code out of this is, perhaps, easier.
Anyway, I guess I am asking primarily because I want to see if anyone has a good way to backup a Bitcoin Core wallet on a physical medium (paper ideally).