TL;DR
You can add up to 32 items to Apple Find My, including shared items and accessories, like Chipolo. Google's Find My Device doesn't have a publicly stated limit for the number of Bluetooth devices you can add, but we have successfully tested it with more than 32 Chipolos added.
For the Chipolo app, we recommend adding a maximum of 6 Chipolos if you use an Android device and a maximum of 9 Chipolos if you use an iPhone. We suggest you add only those Chipolos where you need the extra features (like Call Your Phone) the most.
Limitations on Android
The Find My Device app regularly scans for nearby Chipolos but does not connect and maintain active Bluetooth connections most of the time. It only connects intermittently or on specific user actions, like trying to find a Chipolo nearby (and Play Sound on it). This concept allows the core functionality of the app to scale to many Chipolos, and we haven't yet found a practical limit to how many you can add and work with during normal use.
Once you add a compatible Chipolo to the Chipolo app as well, the Chipolo app will maintain a persistent BLE connection with the Chipolo to allow features like Call Your Phone and Out of Range Alerts to work seamlessly.
Unfortunately, mobile phones do not support unlimited simultaneous BLE connections, and we usually suggest having only around 6 connected Chipolos in the Chipolo app. In other words, if you have more than 6 Chipolos actively connected to the app at the same time, you might observe issues when trying to use the Find My Device app or other Bluetooth-related features on your phone. This can vary between different phones and Android OS versions. On some phones, you can easily connect up to 10 Chipolos simultaneously.
You can, though, use more Chipolos if they are dispersed across different locations, and the Chipolo app will never connect to more than ~6 at once. There is no inherent limitation in the Chipolo app itself regarding the number of added Chipolos; the problems only appear if the app tries to connect to too many Chipolos at once and exhausts system resources.
Limitations on iOS
The Find My app regularly scans for nearby Chipolos but does not connect and maintain active Bluetooth connections most of the time. It only connects intermittently or on specific user actions, like trying to find a Chipolo nearby (and Play Sound on it). This concept allows the core functionality of the app to scale to many Chipolos. Apple limits the amount of items in the Find My app to 32, as referenced in the support article Add an AirTag to Find My to keep track of personal items - Apple Support.
Once you add a compatible Chipolo to the Chipolo app as well, the Chipolo app will look for two different types of beacons per Chipolo to allow the Call Your Phone feature to work. As the system limit on iOS is 20 different beacons per app, you can reliably enable the Call Your Phone feature on up to 9 Chipolos at a time. The final two beacon slots are used for other purposes.
There is no other limitation in place, so you can still add more than 9 Chipolos to the Chipolo app and use on-demand features like changing the ringtone or taking a selfie.