Handing over a physical driver's license exposes everything printed on it to the person checking it. If someone only needs to confirm that you're over 21, for example, they may also see your exact birth date, home address and license number. An mDL can be more selective. The standard supports broad age statements such as whether someone is over 21, allowing a compatible verifier to request that answer rather than seeing the person's complete date of birth.
Apple and Google add their own protections as well. Apple says you can review requested information before sharing it, and in-person presentation requires authentication with Face ID, Touch ID or an applicable accessibility method. Driver's license and ID data is encrypted, and you don't need to hand your phone to the verifier or unlock it.
Google says its US driver's licenses and state IDs are encrypted and stored locally on the phone rather than in your Google Account. Google Wallet also shows the requested information before it's shared and requires you to authenticate.
Those controls don't make a digital license automatically safer than a physical one, but they can give you more control over what you reveal.