Minecraft Server Make sure that other people don't destroy blocks?

I have a Minecraft server that clears all people who join and puts them in survival mode, but it is still possible to destroy blocks from the lobby, for example. How can you turn it off, so that's only Op's blocks can destroy?

Would rather recommend worldguard and worldedit, because you can use them to create different regions with different permissions and not as one-sided as with commandblock.

In addition, you can also use it to set the OP authorization so that nobody can access the ingame. A super safe solution.

Thank you