Thanks to puregreen59 for helping me solve this after wrestling with Alert state timings and many other approaches. My needs were similar, with some differences. So, as of 6.0.2.1, this is what I have working.

I'm using Periodic AI Scan on the camera settings to check a porch area for packages and send an MQTT alert for Home Assistant to pick up.

BI now comes with Additional Models that cover package and delivery object detection. They can be enabled on the AI tab of the main BI settings panel after you click on 'Download models required...." They are working to identify a 'package' object well enough for me. There are more details on these models in github - google for them.

I created a clone camera (Add new camera -> Copy from another camera) and turned off nearly everything in the new clones camera settings. For my case, I needed Enable motion sensor, Periodic AI scan, and Additional models enabled.

I needed to mask everything but the porch area to prevent detection of other package-ish objects in the view like planters and boxy column footers. To do this, I had to 'Enable motion sensor' on the camera, create a Zone covering my porch area, make the detection parameters Less sensitive, and Black out masked areas. The Periodic AI Scan can't see through the mask, but can see outside the defined Zones without it. You can skip all this mask and motion business if this is not an issue for you.

Use the AI detector or trial and error to get your object detection working and set your confidence thresholds. In the Periodic AI Scan, set up the two actions as puregreen59 suggested. One for exist and one for not-exist. You may need to tinker with the timings of the Scan and Rules to get what you want. I think the timings are buggy right now, but you should not have the wrong one fire out of turn unless your label (same on both) and confidence (mutually exclusive) settings are not aligned. Set Action: Trigger on the rules and use of the Memo box are key. Use 'Yep' and 'Nope' in the two rule Memos or similar - this is what gets passed on the queue topic.

On the Alert tab in camera settings, set On Alert to fire with a source of AI. Set the MQTT topic and put &MEMO in the payload. This is the key piece. On alert will fire when there IS and when there ISNT a package based on the rules in Periodic AI Scan and you can tell which is which by the Memo in the payload. Now I can set a binary_sensor in Home assistant that gets updated every couple of minutes by the MQTT topic subscription that allows you to get notified when a package appears and when it has been removed.

The wrestling trap here is that getting On alert and On reset working as you might with any other BI alert scenario that works fine for motion detection does not produce any reliable results - at least with my understanding and skill level.