This list is all the MNO & APN combinations that support the Caps & Alerts functionality described here.
AT&T
Bouygues (on private shared APN)
Conexa-OS
Deutsche Telekom
DT-IOT
EE (except custom infrastructure)
KPN (on arkessahd.com, arkessa.com and wlapnlns.com APNs)
Manx
O2
Orange France
Orange Spain
SFR (on private shared APN)
Telenor & Telenor Denmark (on private shared APN)
Three UK
Vodafone - including UK, Spain and Global