Valheim server is visible but joining always times out

Valheim can see the server or lobby, but joining either times out or returns to the menu. Other players can sometimes connect.

What should the host and client check in order? I need a practical list for version matching, mods, firewall, ports, region, and Vulkan mode, world saves, dedicated servers, and large-base performance.

Check host and client in the same order:

1. Confirm identical game versions.
2. Remove all mods for a clean test, including server-side dependencies.
3. Verify files on the player who cannot join.
4. Test a direct invite and server-browser join.
5. Check host firewall/NAT and confirm the server port is actually listening.
6. Back up the world before changing server files.

For Valheim, pay attention to Vulkan mode, world saves, dedicated servers, and large-base performance. Do not wipe the world until a new empty test world proves the save itself is the problem.