What changed
Use unstable-events.net as the server address. The old entry in your multiplayer list may still point somewhere else, so edit it or add a fresh server instead of pressing Join on the old card.
Update Java
Open Multiplayer → Add Server, name the entry Unstable SMP, and paste unstable-events.net into Server Address. Do not add a port, a slash, or https://. Choose Done and join from the saved entry.
Update Bedrock
Open Play → Servers → Add Server. Use the same address and enter 19132 in the Port field. Some console editions do not allow custom server entries.
If the old address is cached
Delete the old saved entry, restart Minecraft, and try again. If the client reports Unknown Host, compare the spelling against the server IP reference. If it reports an outdated client, check that your release is in the range 26.3–1.21.11.