As far as I'm aware it is possible to use Frida without rooting, by using Objection https://github.com/sensepost/objection

> Patch iOS and Android applications, embedding a Frida gadget that can be used with objection or just Frida itself.

This is the key thing, and the part that will change next year: previously, you could unpack, patch, and repack an APK with the Frida gadget and install it onto an Android device in Developer mode, while the device remained in a "Production" state (with only Developer mode enabled, and no root). Now, the device would either need to be removed from the Android Certified state (unlocked/rooted) or you would need to sign the application with your own Developer Console account and install it on your own device, like the way iOS has worked for years.