Mobile voting hasn't had much traction in the US, but that apparently isn't for a lack of trying. The US Postal Service has confirmed to The Washington Post that it secretly developed and tested a blockchain-based mobile voting system ahead of the 2020 election. The project was purely "exploratory" and was abandoned in 2019 after University of Colorado researchers discovered security flaws, including the risks of impersonation, denial of service attacks and "techniques" that compromised privacy.
However, it might be the lack of transparency that raises the most concern. The USPS didn't coordinate with other federal agencies, and it asked the university to sign a non-disclosure deal that prevented them from naming the institution involved. Election security officials just learning of the blockchain voting project were worried it might erode trust in the democratic system already hurt by unsupported claims of significant fraud during the 2020 vote.
The Postal Service has considered electronic voting before, but centered its attention on those who can't easily vote, such as soldiers and people with disabilities. This was a practical exercise that could have applied to a large swath of voters, not just a small group that can't realistically use mail or in-person balloting.
The end result was the same with or without the test: the 2020 election continued to rely on paper ballots, and federal agencies focused more on establishing a paper trail to reduce the chances of Russia and other actors from tampering with the vote. The revelation shows there wasn't a completely united front, though, and suggests vote-by-smartphone efforts aren't about to take off any time soon.