How can technical folks at the individual contributor level upskill themselves in non-technical aspects of the business?

If you are talking strictly about the business, there are multiple avenues, from community college courses in the area you are supporting to what I personally have employed in my career - a day in the life. Whenever I changed roles or went to a new company, I would request from leadership of various business areas to shadow some of their personnel. I would shadow everyone from pickers in the warehouse to accounts payable clerks - just to understand the pains in daily life for our IT customers and also spark ideas for how to help/improve various processes. 

A simple starter is through reading of your own outward facing website. Do you know all the products? Do you know the benefits compared to competitors? If public have you read all the filings? Listen to the public earnings calls, they are different from the town halls for employees

All this can be done without even telling your boss

Learn from their leadership. Talk to clients about their business processes.

Before I began my first role as a team lead, I would shadow my team lead at the time and learn about what they were doing as much as possible. I’d observe how they were running the team and the workload, and I got firsthand experience of what the role would be like. Another option is volunteering to take on a bit more responsibility within your team beyond the day-to day-coding. 

The most essential skills you need to build are related to people management, which can’t be learned by shadowing because you're not part of those one-on-ones. You can do one-on-ones with your colleagues, not for the purpose of people management, but to build rapport and get an understanding of what those conversations are like.

Management training is always available through courses and books, but if your company provides future leaders with management training, you should take advantage of that. Because when you move into roles where you have line management responsibilities, it is a completely different job. That's something that I've always advised to budding team leads or people managers. I’ll ask, "Is this what you want to do? What are your expectations? What do you think that role actually means?" It’s an opportunity to align their expectations with reality.