Toyota prius 2005 in year 2020

welcome!
hard to say from n/a, what does the oil cap say?

did you just get it?

 

I use Full Synthetic 0W-20 on West Coast of US where freezing temps are rare...

 

I use 5w-30, which is what the filler cap says to use.

 

smart

 

Agreed. Just use what the manufacture says.

 

I noticed that the oil stayed cleaner and lasted longer when I switched to 0w-20 full synthetic... Seemed like gas mileage on long freeway drives was slightly better too.

 

The car is 15 years old.
Just out of curiosity, how many miles does it have on it ?

Unless there is some evidence of excessive oil usage, you should use what it says on the filler cap.

If there IS high oil usage, then switching to "high mileage" oil would be a good idea. That probably is 10W40.