Apple Car Play

No, unfortunately there isn't any way to do so without replacing the head unit.

That said, i have seen an adapter on ebay that lets you put a 2018+ head unit into a 2016-17 prius. (search for this on ebay "Toyota Radio Retrofit Adapter - Entune 2.0 (pre-2019) to Entune 3.0 Carplay")

Though i'm not 100% sure it works with the prius.

 

There actually is a way for the gen 4 pre-facelift models (Entune 2 and Touch 2). There is an adapter from a company called Carabc which hooks into the original radio's wiring harness. I installed this in my 2016 a few weeks ago and there are multiple YouTube vids on this.

 

How about some details or link to some more info? We aren't trying out for "Ghost Hunters" here, ya know.

 

The unit I built into my 2016 a few weeks ago is from a company called Carabc. Installation was done in under 30 minutes. There are also other companies offering a similar device, but the Carabc seems to be the cheapest.

Picture quality is a bit worse than the native nav app because it hooks into the backup camera feed (touchscreen is working just fine with it), but this is a tradeoff I'm more than willing to make for wireless CarPlay.