After you uninstall an addon, shouldn't it be also removed from SBSettings' Mobile Substrate Addons menu? For instance, I uninstalled Clockify, but it still has its on/off switch in that menu.

If you had already turned it off using SBSetting then it will NOT be removed because the OS is completely unaware of any adjustments you have made in SBSettings.

To remove it completely, turn it ON in SBSettings, install the tweak again in Cydia, then check SBSettings again. You may have one or two entries for the same tweak. Regardless, make sure they are both turned ON, then remove the tweak using Cydia. That should remove it fully.

Turning OFF mobile substrate tweaks using SBSettings should only be used as a temporary measure, and you should always remember to turn them back ON before trying to remove the tweak.

Ha, thanks for the advice, that's exactly how it happened. (At first I turned it off as I didn't like it, and later on I uninstalled it.)

What's the relation between turning some tweak off, or disabling it, within ("official") Settings, as opposed to the On/Off switch in the aforementioned SBSettings?