The term "15021" likely refers to a specific version of a YouTube IPA (e.g., version 15.02.1). Users search for "verified" versions to ensure the app is safe, functional, and won't lead to account bans or malware infections. However, downloading IPAs from third-party sources carries inherent security risks.
Trust the developer certificate on your iPhone under Settings > General > VPN & Device Management . Risks and Limitations youtube 15021 ipa download verified