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If you made room on your internal storage as requested, AND if your iPhone is connected to a reliable a fast wifi network (no personal hotspot, no VPN) it should perform the update.
If the issue persists, or if the iOS version currently running on your unidentified iPhone model is very old, try to update it via computer (if you don't have a computer borrow one from your friends/neighbors, or ask for help at an Apple Store or Authorized Service Provider), then learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.
If you still get no help, contact Apple Support directly, using this link:--> Get Support
Regards
Giulio