Hi @Zahran23. I see from your other thread that you've covered some of the standard steps already.
Unsure if you've had a look in Settings > Device Care > Battery > 3 dots (menu) > Settings > Sleeping apps, to see if the Play Store app is on that list. If it is, then you could temporarily remove it from the list whilst you're dowloading large files; and add it again, if you want, when you're done. (You can do similar for other apps you temporarily want to keep from sleeping too BTW.)
Sorry about the delay in getting back to you, @Zahran23!
There should be a 'Stay awake' option in the Developer options menu that'll keep the screen from sleeping whilst the phone is charging - so hopefully you'll be able to download large files whilst the phone's on charge.
If you don't have Developer options enabled: Settings > About Phone > Software Information, and click on 'Build Number' seven times, and it should tell you that Developer mode has been enabled. If you go back into the main Settings menu, Developer options should be right at the bottom, click into that, and toggle the 'Stay awake' option to either on or off as you need. (You can also toggle Developer options off and re-enable as per the above method if you wish to.)
