You may have noticed that even if your block's texture is transparent, it still looks opaque. To fix this, override getRenderLayer and return BlockRenderLayer.TRANSLUCENT:

class MyBlock extends Block {
    @Override
    public BlockRenderLayer getRenderLayer() {
        return BlockRenderLayer.TRANSLUCENT;
    }
 
    //...
}

You probably also want to make your block transparent. To do that, use the Material constructor to set blocksLight to false.

class MyBlock extends Block {
     private static Material myMaterial = new Material(
            MaterialColor.AIR,   //materialColor,
            false,   //isLiquid,
            false, // isSolid,
            true, // blocksMovement,
            false,// blocksLight,  <----- Important part, the other parts change as you wish
            true,//  !requiresTool,
            false, //  burnable,
            false,//  replaceable,
            PistonBehavior.NORMAL//  pistonBehavior
    );
 
    public MyBlock() {
        super(Settings.of(myMaterial);
    }
 
    //...
}

First we need to make the block appear invisible. To do this we override getRenderType in our block class and return BlockRenderType.INVISIBLE:

    @Override
    public BlockRenderType getRenderType(BlockState blockState) {
        return BlockRenderType.INVISIBLE;
    }

We then need to make our block unselectable by making its `outlineShape` be non-existent. So override getOutlineShape' and return an empty VoxelShape'':

    @Override
    public VoxelShape getOutlineShape(BlockState blockState, BlockView blockView, BlockPos blockPos, EntityContext entityContext) {
       return VoxelShapes.cuboid(0,0,0,0,0,0);
    }