There are multiple issues with this idea. First, I just don't think you can really tell that from this perspective. That's just thinking too far into the future. This sort of argument is likely to look like a Great Horse Manure Crisis of 1894 [1] to our descendants.

[1]: http://www.historic-uk.com/HistoryUK/HistoryofBritain/Great-...

Have you actually considered how many people it would take to use all energy that sun and future tech can provide? I'm sure no human being can give you even a rough estimate.

It's not like solving aging will break markets. There's a balance between supply & demand, which will indirectly regulate birth rate due to parenting costs.

Universe is really vast, if not infinite. And when we have more people, alive, and doing meaningful things while automation takes over menial tasks, it's really going to make us tackle other problems faster, like transportation.