itch.io

1. Go to your device settings and tap Apps & Notifications (or Apps in older versions of Android).
2. Tap the three dots in the upper-right corner.
3. Tap Special access.
4. Tap Install unknown apps.
5. Tap Chrome  (If you're downloading from Google Drive, make sure to turn on permissions for the file manager and Google Drive you're using)
6. Move Allow from this source to the On position.

If this is the first time you are installing apk, you will have to do this setup. 

I'm sorry.