If you think the AF focus field line width is too weak, that’s because Olympus ships this setting with 75% So 25% transparency.
If you increase the value to 100%, the lines get clearer and it’s easier to see them
In addition, it is also possible to display the line in different colors (for example red).
You will find the setting here:
Menu D3 –> Framing Guide Options –> Display color0