Ask which edition, not just which device
Java Edition and Bedrock Edition host different multiplayer sessions. Windows can offer both, so two players using computers are not necessarily using the same edition. Confirm the edition shown by each game before arranging a world or Realm.
Match the play session
Vanilla Java players join Java worlds and servers; Bedrock players join Bedrock sessions across supported devices. Do not promise native Java-to-Bedrock cross-play. Servers using third-party bridges are a separate setup with their own support and behaviour.
Keep content and commands in context
An add-on, world pack or command written for one edition is not proof of support in the other. Check the product and version labels before purchasing or copying a command. On consoles, online play also depends on the platform subscription and account multiplayer permissions.