You take a few products from open source, integrate, customise. It’s still called development, and it still requires skill – that is is you want your test framework to be stable and grow. It needs skill, as you need to minimise product-dependencies ongoing, or you can quickly get lost in spiral of dependency failures, as you update core framework.
You can chase rainbows for the ultimate test automation tool – there are those using open source, with same dire “all your problems are over” style taglines for their SaaS.
While you are chasing your rainbow, I will have built a framework and maintained it for resusability and open to all to use – tech and non-tech people alike. By trusting a third-party vendor or SaaS, you constrict your team immediately to work a certain way. It limits creativity and relevance.