The problem that your product owner cannot see any value in replacing/understanding/modernizing that piece of software, but should it fail, the heads would roll, speaks of a bigger problem in your organization than an ancient piece of software.

You have been able to put it in a container and it’s running, so unless the kernel itself changes drastically so old libc will just stop working, it’s going to be able to work unchanged for a decade more.

But the communications problem between management layers is way bigger than that, and could probably bite in some other situation.