How to sign the Android application so that it is preloaded in the phone and not published in playstore so that the problem of protection block during the installation is not reproduced?

When we try to install the .apk that is signed by putting it in the file manager of the phone and not published in playstore, we have a problem,
"Play Protect does not recognize the developer of this application, and unknown developer applications can sometimes be insecure."
By clicking "Install anyway", we can install the apk, but we do not want that pop-up window to appear.
We need to preload the apk on a phone without publishing it.

We have done it in debug mode and we have no problems, but when we did it in launch mode and signed it, the problem arises. Also, from the second time, the problem is "The application is not installed".
We have seen all the solutions around the web in the stack overflow, we found a similar link, but the problem is different here. Since we do not have to publish it on Google Playstore but preload it on a phone, the solution to publish the application so as not to get this problem from Play Protect will not work.

Expected: The problem of blocking Play Protect should not appear even if we do not publish it on Google Playstore.
Real: We are facing a problem of blocking Play Protect when we sign the application and try to download / preload the .apk.