My guess, if you just wait it out, this situation will resolve eventually. You still have the loaner car, right? Just use that in the meantime. I expect your mechanic is having trouble securing the required replacement parts, which is a pretty common thing these days. Another mechanic would likely have the same delay. Even family members of the Car Talk team report having the Covid-era supply-chain problem.
I expect you’ve already learned it is best to do this sort of business w/an actual pro-mechanic, who operates legally out of a well-managed shop, and is in accord with all the various regulations. Get a written & signed price/repair-time estimate before handing over your keys.