> What problem does it solve that hasn't been solved by other people?

nothing. Except for "portability" arguments perhaps.

Java has had security managers and access restrictions built in but it never worked very well (and is quite cumbersome to use in practice). And there's been lots of bypasses over the years, and patch work fixes etc.

Tbh, the OS is the only real security you could trust, as it's as low a level as any application would typically go (unless you end up in driver/kernal space, like those anti-virus/anti-cheat/crowdstrike apps).

But platform vendors always want to NIH and make their platform slightly easier and still present the similar level of security.