You can register using a non-UAE phone number only if you sign up with UAE PASS.
For standard registration and sign-in via SMS or WhatsApp OTP, only UAE phone numbers (+971) are supported.
If you signed up using UAE PASS, your account may have a non-UAE phone number. However, for future OTP-based sign-ins, you’ll still need a UAE (+971) number. You can update your phone number later to continue signing in without issues.