You are trying to get a product business off the ground. It has been an uphill battle due to lack of funding, necessary to scale the business. Can't raise money due to the industry and business not fitting the typical VC blueprint. So you continue to bootstrap.
You are paying the bills with consulting. Maybe you have some rental income. You need to plug the retirement hole.
Do you invest in your product business and continue adding to the risk or do you just buy ETFs and hold?
You can also "yes and" this. Invest in the startup, by some investments, etc. Multiple streams of returns that are uncorrelated is the holy grail formula for investing [1].
It sounds like you believe that lack of funding is the root cause of your inability to grow/scale. Almost always, it is something else first and not that.
If you have to ask this question, you probably know the answer already. Go invest in the other stuff and perhaps reconsider what you are doing with this product/business.