Can I get a replacement for screen under my warranty? I didn't have a tempered glass as there was no good screen protector available
Based on your description, probably not. Normal wear and tear is not covered by the warranty. This is the US Warranty, so yours might be slightly different. https://www.asus.com/support/images/upload/warranty/us_ZenFone.pdf
I'm referring to Section 6 (d).
Can I get it replaced outside warranty ... By paying ofcourse directly in one of your repair centers ?
Yes, that should be possible. Of course it is dependent on whether they have parts, which is not guaranteed due to the Coronavirus.
Just a heads up, the display is the same component as the exterior glass, which means it is probably an expensive part. Check with the repair center for a final quote, but it likely will not be cheap.
Aah will wait for it to get a bit more scratched up I guess.