Java Edition players have their own version of Realms and can play with other Java players. Bedrock Edition is a better option when it comes to players looking for crossplay in Realms.

Java players and Bedrock players can’t team up and play together, even if they are both on PCs. The two versions just can’t work together. If you have a friend or group that plays Java, then ...

For the Java Edition, cross-play with the Bedrock is not officially supported. However, tools like GeyserMC allow the Bedrock players to connect to the Java servers easily.

While any user of the Java edition can join a game with any other Java player, and any Bedrock player can play with any other Bedrock no matter what console they’re on, Javas and Bedrocks cannot ...

Microsoft's official announcement post also references cross-play, which would seem to imply that Java and Bedrock Edition players will finally be able to play together.

Microsoft explains more: "The Bedrock Edition of Minecraft is available on consoles, mobile devices, and computers running Windows. Cross-platform play is supported with other Bedrock players.

For the Java Edition, cross-play with the Bedrock is not officially supported. However, tools like GeyserMC allow the Bedrock players to connect to the Java servers easily.