Bedrock Java servers exist for one reason: Java and Bedrock players can join the same multiplayer world. That lets a group mix PC Java with console, mobile, and Windows Bedrock without splitting into separate servers. Most of the time this is done by running a Java server and letting Bedrock clients connect through a compatibility layer.
The gameplay loop is standard multiplayer Minecraft, but you feel the seam between editions in small ways. Some UI prompts differ, a few items behave oddly, and redstone or mob timing can be less predictable for Bedrock clients on a Java ruleset. Well-run cross-play servers plan for that by keeping mechanics simple and consistent, and by avoiding systems that depend on fragile, edition-specific behavior.
Where this format really earns its name is identity and input. Bedrock shows up as Xbox gamertags, Java shows up as Minecraft usernames, and the server has to map both cleanly to ranks, claims, punishments, and economy. Add in touch, controller, and mouse inputs and you get PvP and movement that do not feel identical even in the same arena. The better communities acknowledge those differences with clear settings and fair expectations instead of pretending every client plays the same.
