I figured it out!
After some further debugging I found that even when omitting the pushType the activity still wouldn't start on "older" devices. Then I stumbled across this sentence in the documentation of Activity.request(attributes:content:pushType:):
"If your Live Activity displays image assets, the system requires them to use a resolution that’s smaller or equal to the size of the Live Activity presentation for a device. If you use an image asset that’s larger than the size of the Live Activity presentation, the system may fail to start the Live Activity. For information about the sizes of Live Activity presentations, see
Human Interface Guidelines > Live Activities."
So it turns out the problem was that I'm using 500x500 image assets in my Live Activities - which is just inside the range for iPhones 12 and up, but too large for iPhones older than that.
Topic:
App & System Services
SubTopic:
Notifications
Tags: