you can probably build it yourself

Well, I mean, I can. I don't know about you, maybe you suck. But if you don't suck, I bet there's a bunch of things that you're paying for, or considering paying for, that you can just build yourself. There's probably libraries and architectural components, SaaS products, IaaS products, MarTech products, CRMs, CSMs, CDPs, PDQs, PCPs, ABQs, DBTs, ORMs, and PBJs that do 1000 things you don't need, and 1 thing you do need almost the way you want it to but not quite. If you think you know what you need better than a thought leader, you're probably right, so just build it. If nothing else it's a reasonable intermediate step to help you understand what you actually need.

Like, don't built it if it's gonna take you 6+ months, don't be stupid about it. But if you think you can hammer out your personal MVP in 2 weeks, do that first before you start talking about build vs buy or using an open source project that has 400000 stars. Either you'll hit the limits of what you built and realize you need something more robust that you can't build, or you won't and your 2 weeks mini project ends up driving disproportionate value. Just make sure you have an exit strategy either way.