If you're making enough money, you can hire a designer every now and then to tell you where your UX suffers and how to fix it. No investors necessary.

(or: just solicit feedback in a space frequented by designers, and harness the power of being wrong on the internet ;)

It is very straightforward to hire UX designer in a contract, or even just ask ChatGPT to design an interface that is better than a software engineer's minimum effort (and possibly experience) in UX.

It is quite possible that this will be the case.