Was there anything the Germans could have done to make Enigma foolproof encryption like we have in the modern day?

Had they not used a reflector pin in the encryption (simplified encrypting/decrypting a message using the same rotor configuration) it would have been far harder to crack, because the pin ensured that no letter could ever encode itself and that greatly reduced the search space

Also today there is no foolproof encryption if you make misstakes (or if an unknow attacker knows more about math than you do, or made a working quantum computer)

And what nazi germany could have done back then, to not have it broken would have been very simple: not using prussian style of communication, meaning all the messages followed a certain pattern with certain keywords. Since the british knew those keywords and pattern, they had something of an angle to break it. (Parts of it are covered in the article)

Or of course use another layer of encryption (but that requires a simple redesign) which would have made the decryption not useful in a timely manner.

Iirc, veritasium video said it was the weather report at the beginning of the message that fueled quicker decryption. So, not following same letter format each time might have helped.

The fact that the Enigma never encoded a letter as itself was a significant flaw in the design, which could presumably have been avoided.

Better training for the operators would also have helped, e.g. don't start every message with "Heil Hitler". Some of the services were much better than the others IIRC.