A developer preview of Wiki.js 3.0 is now available for advanced users that want to run it on their machine and try it out. This is NOT a beta and should NOT be used in production or in a publicly-accessible environment. Make sure you fully read the notice and instructions first and understand the implications.
A beta will be available in the coming weeks / months, once more features are stable and working.
Detailed instructions are available at the project README on GitHub. You can either run it using VS Code Dev Containers (recommended) or natively on your host.
Make sure you fully read the instructions first.