Just updated to Android 10 and found apk cannot be installed from just any file manager or other apps. The solution is simple and given below.
Go to setting of Android -> Storage -> Select storage -> Browse and install apks.
Or
Google's own app called "Files" can install apk files. Download files apk from playstore and install backup apks. This feature is extremely important because many apks are no longer available on playstore due to various reasons. For example my i own games i unpublished from store. There may be other apps which can install apks.
