I don't think it's that God couldn't create a universe without evil, it's just there's a process for making us good AND retaining our freewill.
So he's letting us help to create a universe without evil...
Evil is necessary in this process, but evil is really just God "occluded" - Satan is in this sense working for and with God in this process of teaching humans about good, hence the line "God works in mysterious ways"... We don't know the process, which is why it's faith-based.
It's like yes, your parents could give you a lifetime of pocket money all at once, but they're not going to because you have to learn patience, self-discipline, and saving up for the things you want (or can afford). You have to make choices in that process to learn about those things.
Humans are temporal... God is not.
So for God, God created a world without evil in which humans have freewill... It's already been done, instantly for God.
But we don't live on the same temporal plain.
Claiming God can't do it, is like being the kid asking for ALL the pocket money at once. Parents could do that, but they're letting time and your own temptation teach you the lessons.
That's part of the mysterious ways. But in faith, outside of time, and with the right beliefs and choices, a world without evil where people in your life still have freewill already exists... It's up to you to live there in it, in time.
You're assuming that the creation of suffering is evil when God does it - however it could be that if heaven exists as a place in the future where everyone's all good with what happened...
...then it might not be evil when God does it, it might only be evil when humans do it (because we're not capable of doing it in a way that's consciously creating heaven (where everyones okay with what happened) as a result... We can't arrange souls like God can. We can't live or operate outside of, or beyond time like God can.
...also, not that anyone asked, but personally - I'm an atheist. I'm just seeing how far these arguments can go with provisos like heaven, God as a time lord, and souls/at-birth soul agreements.
Oh, also God can patch up or fix up, or factor in suffering humans create, because being able to predict that something is going to happen isn't the same as causing it. Eg. I know the sun is going to rise each day up until an expected sun-death... Even if humanity creates the ability to make the sun rise, it doesn't mean the sun is currently controlled by us. Yet it's still predictable.
Still, the (theoretical) fact remains that god knows about the suffering and lets it happen. Whatever the goal is, if he's omnipotent he should be able to reach it without having suffering. If he can't, he isn't omnipotent. If he doesn't want to, he's not good.
He mentioned before that maybe the process for making humans good and retaining free will necessarily requires evil to exist. It's possible that by definition, suffering must exist, not that God couldn't do it. Kinda like how, by definition, you can't make a four sided triangle; it's not that God wouldn't be powerful enough to do that, it's that a triangle requires three sides by definition. Maybe the incorporation of free will requires suffering, even suffering not caused by the choices people make?
A four sided triangle is a verbal misconstruct, because we chose those names to represent different objects - nothing to do with what god can or can't do. They could make all of us believe that four-sided polygons are called triangles, which fulfills the requirement you propose. On the other hand, free will can't "require" suffering, because a requirement would mean there is a rule god can't break, which would mean they are not omnipotent.
But it could be suffering is by nature what allows us to enjoy good. You can't have a human if the human doesn't know not good, because how would you enjoy what you can't appreciate? The rat utopia experiment kinda shows what happens when you introduce a biological being evolved for stressors to a perfect environment. And humans may already be going through something similar but not as bad in developed countries (the lower birth rates, increased depression, etc) as what happened to the rats in the rat utopia.
So essentially what you're proposing is not allowing humanity to exist, and that it's a good thing.
It's not an invalid argument, but do consider some might consider that in itself evil, which brings us to the biggest real question: defining "evil".
An omnipotent god could alter nature in a way that makes us able to enjoy good without needing to suffer. If they can't, they're not omnipotent. If they don't want to, they're letting us suffer unnecessarily, and they're not good.
You technically could, but surprisingly, a lot more people take issues with their entire personality, memories, and consciousness being altered than with their bodies.
Because again, that's what you are proposing as "good".
Don't see how that's what I proposed as good. As time wouldn't exist for god (implication of being omnipotent), there's no reason that suffering ever existed in the first place - no need to change anything on a running system.
True, but there could be a meaning or reason behind the suffering we still don't understand either way is my point, because we still don't understand enough of ourselves or the universe yet to know if it's the better choice either. After all, before the rat utopia experiment, it was assumed having literally every need met perfectly would lead to happiness rather than disaster. It could be that he's done both for reasons unknown to us, creating both our dimension with suffering and one where suffering never existed.
Or there could be no reason at all, and God is an omnipotent being that is neither good nor bad, much like the ancient Greek concept of the God Chaos - they just "are".