Directly after an update, the Volumes item may be empty: When you update to System Monitor 5.7 from an earlier version and the monitor item Volumes is active, it may show a zero value without any menu items.
Workaround: After an update, the volumes item does not show any values until the user has confirmed which volumes to add to the total sum shown in the menu bar. This is currently the correct and intended behavior, but this is not fully communicated in the user interface or the reference manual. Open the control window, navigate to Information Sources > Volumes > Include the following volumes, then click on any of the check mark boxes. After this step, the Volumes item will resume its work. You can fine-tune which volumes to show and which volumes to list in the menu only, without adding them to the storage total.
Monitor items might be placed behind the camera notch of the 18th generation MacBook Pro or may be shown incorrectly when they exceed the notch: If you have configured many monitoring items with a total width that overlaps the position of the camera notch for any of the MacBook Pro models released in October 2021, some items may be shown behind the notch so that their indicators in the menu bar become invisible. When items are wider than the notch or become positioned left to the notch, macOS may show them incorrectly, without content or with wrong widths.
Workaround: This is a known defect of all versions of macOS 12.0. Update to macOS 12.1 or later to fix this problem.