Local Co-op Games for One Laptop: Check the Controls Before You Buy
Two players, one laptop and one keyboard are a specific setup. A local co-op label tells you that people can play together on one machine, but it does not tell you what inputs the second player needs.
Start with the input arrangement
For a shared-keyboard candidate, look at the original Overcooked on PC and check its split-keyboard instructions for your edition. The players divide the keys between them. If the keyboard feels cramped, try a keyboard and controller instead. Before buying a sequel or bundle, check its own control documentation; editions can differ.
When each player needs a device
For Stardew Valley split-screen, check the local multiplayer instructions for your platform and prepare a controller for the additional player on PC. Check whether the game needs a cabin or an existing save setup before inviting someone to play. For any new game, confirm it offers local multiplayer on the PC edition you intend to install.
Run a two-player check
At the join screen, test each input separately. Then have both players move diagonally and press an action key at the same time. Missing inputs only during simultaneous play can indicate a keyboard key-combination limit. Try remapping one player or moving them to a controller before troubleshooting the game itself.