To compile the code, click on the "Solidity Compiler" tab in the left-hand sidebar. Make sure the "Compiler" option is set to "0.8.4" (or another compatible version), and then click on the "Compile ...

To compile the code, click on the "Solidity Compiler" tab in the left-hand sidebar. Make sure the "Compiler" option is set to "0.8.9" or more , and then click on the "Compile HelloWorld.sol" button.