we discovered that the share of solo founders has nearly doubled between 2018 and 2026 to 39 percent of new startups

That seems like a less interesting metric than the percentage of successful founders who go it alone. If there are just more startups because founding something alone is much easier, but you're no more likely to succeed as a solo founder, then all that's changed is the number of failing startups. That's not a great ad for starting something without a someone to share the burden.

FWIW in my experience with startups it's the relationship between founders that keeps the product on track and heading in the right direction. Founders keep each other honest (mostly) about whether something is worth building. When someone is going solo they build what they want, which goes brilliantly if they have taste and experience of their market, and horribly when they don't. And it's much more common to see the latter.