Unfortunately, this can just another vector on which to be hacked or exploited. Both from hacker to the governments running it. Also has the usual assumption of everyone having a smart phone and it always being available. To everyone either having iOS or Android and nothing else.
The usual issues with these kind of digital solutions.
I will take a Richard Stallman pun/joke, "I am not against the government or the state, and not just because I have a Pro-state gland" groans!
ID's are a common thing, drivers licenses/proof of age cards being the most prominent thing. That is fine enough, but having it all tied to what is a significantly more fragile digital and exploitable at a distance systems - it is one of those that things that looks like, those that push these things are looking at only the upsides but ignoring the flaws.
What is the back up for if/when this system has a failure. What happens if your phone runs out of power for the day? And if your phone of choice doesn't support these ID's, what then?
This does come down to the idea of the technology essentially gets forced on you by government, you have no option to opt out. Unfortunately, at this point it all starts to sounds like an anti-vax argument.
Alas this is something Ted Kacsynski wrote about, technology essentially robs you of autonomy because if others end up using it, you are forced to keep up or be left behind. I don't completely agree with that sentiment as there is the option of concurrent technologies - but it rare that happens.
The usual issues with these kind of digital solutions.