For example: Open source database that works on one machine. If you like it and want want to scale up, you can pay for the replication and authorization features with paid support.
Just ask Docker. There's thousands of companies using Docker Desktop that should be paying for it but aren't. Same for most other Open Source companies with business licenses. Because they set themselves up as an "open source" company, all the villagers revolt when you finally ask to get paid, or stop allowing competitors to steal your lunch. You can survive, but it's very hard, and eventually they die away. (But that's also because most software gets replaced after a decade)
You have to treat your business as a business first and foremost if you want to remain profitable and competitive. You can use Open Source for your business, but you will not survive for long if you're hoping people will pay you just because they can read your code. Eventually reality, and competitors, come knocking.
I’m a pretty rusted on Odoo developer, this has been their business model for years and it’s worked thus far, even when facing off with the likes of the SAP and Dynamics of the world.