Verify NSStatusItem rendering via defaults preferred-position keys
Confirming whether a macOS app is actually drawing menu bar items
When a menu bar app appears invisible, check defaults read <bundle.id> for keys like NSStatusItem Preferred Position <ItemName>. macOS automatically writes these whenever the app successfully registers an NSStatusItem with the system — even if the icon is offscreen or hidden by a menu bar manager. Example: defaults read eu.exelban.Stats showed positions for CPU_mini, Sensors_mini, RAM_mini, Disk_mini, Network_speed, Battery_battery, proving Stats was rendering 6 items that were just being clipped by the notch on an M4 Pro MacBook. Combined with installing Ice (jordanbaird-ice cask) to manage notch overflow, you can definitively separate did the app fail to render from is the icon just hidden.
Before assuming a menu bar app failed to launch, grep its defaults for NSStatusItem Preferred Position — if those keys exist with numeric values, the items exist and the problem is visibility, not configuration.