AFAICT, some wallets like Electrum represents bech32 addresses in lowercase when using the QR codes; nothing wrong just that not all follows the recommendation.
it is not a recommendation to change the letter cases when turning them into QR code, it is an option that exists to server very special cases like if you wanted to print the address on a very small surface like a physical bitcoin otherwise it is best to stick to lower case because the other wallet that reads it may not be as sophisticated to recognize upper case!