While I like the idea of more people voting, I can't see enough benefit from this to outweigh both the risks and costs, both of which would be significant.
So, no. IMHO, neither necessary, nor a good idea.
After all, it's not that great an imposition on modt people, meaning fit and healthy, to reqiire you to get your butt to a polling station once every five years or so, or at an absolute minimum, to be bothered enough to organise a postal or even proxy vote.
Exercising your franchise OUGHT to involve at least a luttle effort and commitment. I'd actually prefer a system where people had to earn the right to vote by performing some kind of public service. Working in emergency services, armed forces, teaching, NHS, etc ought to do it, 'cos goodness knows those doing that an't be doing it for the super-high money. Voluntary service, charity work etc, also qualifies. There no doubt are others.
Everybody else, at a minimum, ought to be able to pass some kind of civics test to at least demonstrate a basic understanding of civics, in order, to EARN the right to the franchise, which us not just a right but a duty, and a solemn and onerous one at that.
To remove even the modest commitment to either orgsnise a poostal vote or getting to a polling station and reducing the serious business of selecting a government to the same level of effort as paying for a cup of coffee with your phone is a retrograde step.
That's what's wrong with mandatory voting. Such systems might force people to vote but they can't force them to put even minimal effort into considering which way to vote.
So while everybody ought to be entitled to vote, if you require a phone app to get you to do so, you don't deserve to do so. Grow some civic responsibility and either go vote or at least put in enough effort to organise a postal vote.
The easier you make things for people, the less they value them.