All apps are not available in every country or region. App availability depends on the country/region settings of your Apple Account (Apple ID) and also on legal, regulatory, or developer distribution decisions. Apple allows developers to choose the countries or regions where their apps are offered.
For example, TikTok is banned in India, so it will not be available for download from the Indian App Store. Similarly, an app that is available in one country's App Store may not appear in another country's App Store.
If you cannot find an app, first check your Apple Account country/region:
Settings → [Your Name] → Media & Purchases → View Account → Country/Region
The App Store region determines which apps, subscriptions, and digital content are available for download.
Changing the device or iPhone model will not change app availability; the Apple Account region is the key factor.Also remember that some apps may be unavailable because of government restrictions, age ratings, licensing limitations, or because the developer has chosen not to distribute the app in that particular region.