No, I’m suggesting a class that can be instantiated as many times as you want, like any other class, which is exactly what a singleton is not, then passing it around everywhere. If you have wildly unrelated things you’d be putting into this class if you just translated your current scheme 1:1, then instead, create different classes for each thematically grouped set of things, and pass them around as needed.

Ideally you should be able to run multiple concurrent instances of any of your classes with a different configuration each.

The goal is to avoid creating dependencies on the configuration objects such that you’ll end up having to be careful about the order in which you call methods due to side effects – that’s exactly the problem created by globals.

Makeshifts last the longest.

I typically see a configuration object as some sort of mostly read-only data store, typically the sort of stuff a singleton is good for... Sure you can instantiate it as many times as you fancy to, but after all isn't the whole ideo of a singleton about sharing the same information ?
I really don't buy this "singletons sucks" stuff, at least for configuration object :)