1:1 Sensor and/or Item Detection

Using Arduino Project Guidance
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Hi, I'm Mark. I like to make things. I'm new to Arduino. I've got a couple robot kits and a learning kit with an UNO and I've worked through all the sensor tutorials and I've started working on a couple of my personal projects.

The goal of this post: Have a sensor (or technique) that can detect if a specific item is touching it, or within a few mm.

The problem that I currently see: None of the sensors that I've found can tell one thing from another. A magnetic proximity sensor can tell that a magnet is touching it, but it could be any magnet. Using Bluetooth, I could detect a specific item, but could not reliably determine its distance.

What I've done: Just internet research so far. I think my biggest problem is that I don't really know what search terms to use. At least I'm hoping it's that, and not that I'm looking for something that doesn't exist or at least isn't commercially available.

Details: I would like to be able to identify that a specific object is where I want it to be. There will be other objects in the area. I don't need to identify those objects, but I need them to not trigger a sensor that they're not 'paired' with. Once the sensor confirms the pairing, the device's (and object's) job is done. Ideally, multiple sensors would connect to a single arduino, but that is out of scope for this post.

For a more 'visual' example. Imagine a board with six evenly spaced sensors attached (like the pips on a die). There are six pencils, they can be identified by a magnet, bluetooth receiver, whatever is necessary to achieve the goal. When ItemA touches, or comes close to SensorA, then a result is returned. If ItemA touches SensorsB-F, or is closer to any of them, nothing happens.

Ideally I would be able to identify the right vs/ wrong items and which item is on which sensor, but that's not necessary at this point.

Responses
If you feel that just offering relevant search terms is enough help, that works for me. Or feel free to be as thorough as you'd like, I'm always happy to learn more.

If I've missed something, please let me know and I'll provide what I can.

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What materials are these mysterious objects made of and how big are they ?

Could you consider using RFID sensors with RFID tags on the objects ?

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Thank you UKHeliBob, I have no experience with RFID other than having heard the term, but that sounds promising. I'll look into it. I do enjoy simple answers.

I was being purposefully ambiguous, because the "mysterious objects" could be just about anything. I can't say that it will definitely be made out of any one material, so the solution has to be material-agnostic, if you will.

Edit: Handheld size, more or less, but various sizes and shapes in that range.

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Consider splitting the object detection and identification

Using RFID would make the material that the objects are made of largely irrelevant. Ideally every object would have an associated and unique RFID but you could consider giving only the relevant objects such an ID and using touch to detect objects

Touch + RFID = "interesting" object
Touch and no RFID = ignore this object and maybe navigate around it

If the object material is suitable then you could potentially use ultrasonic or TOF sensors to detect them and RFID to identify them

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Could the objects be a different color? (You could use the TCS3200, TCS230 or GY-31, color sensor module)

Could you put a QR code on the objects? (Google "ESP32CAM QR Code Reader")

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