Open sourcing a piece of software, especially one that focuses on a broader audience like yours, can convince more people than just developers. The advantages of open source are well-known even among less techy people who aren't necessarily interested in self-hosting the application. It's a good way to quickly earn the trust of people who are initially sceptical of your product.

It shows to your potential users that, even if they decided not to trust the developer anymore in the future, they will likely still be able to use your application. Everyone praised Simple Mobile Tools until the developer sold it to an ad company. But because it was open source, people were able to fork the entire suite of apps to continue using them.

There's also a lot of growth potential. draw.io likely wouldn't be integrated into so many other products if it wasn't open source. It allows them to charge money (apparently) for specific integrations, simply because everyone is already familiar with the product.

Typst is another good example. Their compiler is free and open source, but the web app is not. Certain features of their web app require a subscription, which allows them to pay the bills. But I (and many other people) wouldn't be using and recommending it if the core wasn't open source, because if Typst ever disappears, I still want to be able to compile my documents. Currently this might not matter much for your app since PDF is a universal format anyway, but as you flesh out your product, it will become more important.

It's difficult to monetise open source software, but so much more rewarding if it does work out. And your app being targeted at the general public gives you a massive advantage, since the potential market is so much larger.