Cannot connect: timeout or connection refused

A short checklist before changing network settings.

First distinguish a stopped application from a wrong address or an incompatible client.

Step by step

Check runtime, online state and the startup log. Wait until Minecraft has finished loading.
Copy the current server IP and main port from Overview; do not use the query/plugin port.
Test IP:port directly if a subdomain does not work.
Check edition, client version and any required modpack.
Use the Fix Tool to inspect assigned port and configuration. Keep server-ip on the expected container binding instead of inserting an external dedicated IP.

Check the result

If only one player is affected, compare another network or client. If everyone is affected, collect timestamps and the console error for support.

Important

Do not disable online-mode, TLS checks or account security as a generic connectivity fix.