This can be tricky! It will depend on a triangulation across a number of factors including:
1. The room to grow in your existing product (both in terms of TAM, the competitive dynamics and your current position in the market) -- this will help determine how much headroom you have to innovate on the existing product vs launch new ones. If you have some obvious "low hanging fruit" on the existing product it's usually a sign that there's more work to be done there before launching into new product lines (unless the competitive dynamics push you to do so).
2. The market demand: Most often the demand for a second product will come as a pull from the market vs a push from the company. Look for signs that your buyers are asking for a naturally adjacent solution or expressing a related unmet need that your sales team can't fulfill today. Look for signs that your users expect / are seeking an extension of your capabilities possibly by hacking together a solution themselves, using developers, or seeking solutions through asks to customer support. Look for signs that competitors are bundling a new offering or building partnerships in an adjacent space. These are tell tale signals that the unmet need is larger than you anticipated and the company needs to expand into a new product or service line.
3. The vision of the company and founders (and related funding): Product expansions are usually only possible if these align with the vision of the founding team. What is the business that they set out to build? How has that vision adapted over time? What do your investors expect you to build (a product, a service, a platform, a ...)? This is the less organic, less talked-about, side of product development that does impact how and when a company decides to innovate.