Was there a "Rosetta Stone" found for it?

Yes. That would be the Rosetta Stone. Of course, more can always be said on the matter, so if anyone would like to contribute further material, don't let this compilation stop you! Ancient Egypt is a most fascinating field of study.

• A sadly now-deleted user has an overview of the 'threads to pull' in reconstructing Ancient Egyptian pronunciation;
• u/ajshell1 has a look as to how it was done;
• and u/XenophonTheAthenian and u/CommodoreCoCo have a few comments on scripts and language here.

Some more material in next post because tag limit.