speakers (both)- hardware not working- iPhone 12 mini

Both speakers (and calls obviously)... hardware not working at all on iphone 12 mini. Used phone looks-as new, 99% battery health, with no physical or water damage etc. Made the mistake of buying (in person) used without even considering this kind of hardware/speaker issue before handing over $. Screwed up scammer/seller, oh well, another "cheap life lesson" in the grand scheme of things.

Tried resets including full factory reset, ios update, and any/all relevant settings adjustments etc.

Tested with diagnostic app such as phonedoctor pro which also shows both as failing/hardware issues.

Since the speakers are physically located in different locations of the phone and not (likely/seemingly in my perspective) related to one single loose connector or broken single piece of hardware - what are my chances of being able to fix it as an experienced DIY parts swapper?..

ANY input, experiences, anecdotes or specific advice would be greatly appreciated! Anywhere to look once I open it up, and/or known failed components that could cause all this? Once I solder in the new "loud speaker" with the regular one happen to come back to life. Should I expect to replace both. Thanks in advance!

Note; the iphone 12 speaker recall/campaign does not apply to the 12 mini. Note: either way, this phone is over a year old since first sold so even if it were a 12 not mini, it wouldn't have qualified anyway. I'm looking for repair help not advice to send it in etc.