Share your experience!
Jak odblokować dostęp do aplikacji z nieznanych źródeł, np. apkmirror?
How to unblock access to applications from unknown sources, e.g. apkmirror?
gt
Check if you can find this screen somewhere:
Hi @0522!
Your question has been translated to English as this is an International forum.
As @Strampke mentioned, in Android 8 you need to allow the specific application that you used to download the apk-file from to be allowed to run the file.
You can change the permission in Settings > Apps & notifications > Advanced > Special app access > Install unknown apps > tap on the application you used to download the file and allow it to perform the action.
Let us know if that helps!