Android
Allow Installing Apps from Unknown Sources auf Android
Android treats any app installed outside the Play Store as a potential risk, so it hides the option to install .apk files by default. The permission that unlocks this option lives inside the app that triggers the install - the file manager, a browser, or a messaging app you used to download the package.
To grant that access, go to Tap on Settings ➤ Tap on Apps ➤ Tap on Special app access ➤ Tap on Install unknown apps ➤ Choose an App ➤ Enable or disable Allow from this source. Pick the exact app you used to open the .apk, then switch on the toggle. The setting stays app-specific: enabling it for your file manager does not automatically allow your browser to install packages too.
Skip this step and Android keeps blocking the install with a warning screen, even if the .apk file itself is safe. Once approval is granted, the same app can install or update that package without repeating the warning.
Only enable this for apps and sources you trust. Leaving unknown sources active on apps you rarely use increases the risk of installing modified or unverified packages later.