Trojan virus on iPhone

iOS / iPadOS devices cannot be hacked or infected with Virus / Malware / Spyware if it is updated to latest iOS/iPadOS, unless you have intentionally downloaded spurious softwares or unauthorised apps directly from internet and installed on your device or/and have Jail Broken. 

It (Hacking) also depends on how careful are you in sharing sensitive and valuable informations of your iPhone such as Passcode, Password etc with your friends and family members.

Be careful when sharing the device's sensitive and valuable informations with friends and family members.

Thumb Rules:

1. Don't share Apple IDs
2. Don't Jail Break
3. Don't share sensitive informations pertaining to your device and payment methods
4. Beware of Phishing

See the article https://support.apple.com/guide/security/ios-and-ipados-app-security-overview-secf49cad4db/web

Delete the unidentified app https://support.apple.com/en-us/HT207618

unless you have intentionally downloaded spurious softwares or unauthorised apps directly from internet and installed on your device

iOS is a closed system, an ecosystem, and you can't actually do that.

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6;  HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2

All such messages are scams.

All such apps associated with such popup messages are scams.

Never, never, never download anything based on a popup message.

Delete the app, and verify you have not subscribed to any bogus app subscriptions.