Looking at the links on that page, the only links for 9.0 or 10.0 look to be for the network edition (non oss) I'm not familiar with the situation, but reading

Looking at the links on that page, the only links for 9.0 or 10.0 look to be for the network edition (non oss) I'm not familiar with the situation, but reading through https://blog.zimbra.com/2020/05/is-zimbra-open-source-yes-faqs-about-zimbra-ose-for-you/ https://blog.zimbra.com/2020/05/is-zimbra-open-source-yes-fa... suggests that they do still provide source for at least some portions of 9.x, but they no longer provide binaries or packages. It looks like some components may be missing ("Modern UI"), but I don't know if it's usable without them.