There are less coercive ways to remove barriers to voting. Some US states send everyone ballots in the mail and you have a long time to fill them out, which removes the need to go to a specific place on a specific day; all you have to do is fill it out and put it back in the mailbox. I think that kind of thing is a better option. There are situations where there are strong reasons civic participation has to be mandatory, like jury duty, but if the only real problem mandatory voting is meant to solve is life circumstances leading people to not bother voting, there are a lot of other plausibly effective steps that can be taken instead and it isn’t clearly necessary to do something that invasive.