Coolant Leak in Ford Focus 2015 (EcoBoost)

Hey Petrol Heads,
Faced with bit of a unique situation.
This first started in Nov 2023 with a dashboard message saying "High Engine temperature, stop safely". I ordered recovery and gave it to my mechanic. He had some major repairs a few days earlier so I thought it was related to that (unfortunately I don't remember exactly what the total scope was.) Anyway, he fixed this issue and said it's nothing major. I did not get this message again until March 2024.
This time what I did was wait for the engine to cool down for about 30 minutes and drove to an AutoPro nearby. He mentioned you've run out of coolant and topped it up. He asked me to check it again the next morning and it had reduced below the minimum levels again the next morning.
Again I topped up the coolant and sure enough within 24 hours it disappeared again. This is after driving about 60 kms.
Ordered recovery again and had it seen by another mechanic. He said he did all the pressure tests and checked bleeding as well but could not figure any leak. He claims he even checked the gear oil to see if there's any leak of coolant into the gear box. Also note, this car has seen a transmission replacement in 2022.
Finally he assumes that the coolant is leaking into the engine and passing out directly from exhaust. He said opening the engine to diagnose could be very expensive - said replacing the engine gasket itself is a cost of about 3500 AED. And after that any other flaws, one can never predict.
So his final solution is to check coolant levels every morning or alternate morning, and if it reduces, then top it up with regular water. And once a month, top it up with concentrated coolant. He claims this was how it used to be done in the old days with Fiats etc.
Would love the thoughts of any experts or mechanics on this forum. I do intend to buy another car by the end of the year but don't have the finances to until then. So if this is something I can pull through for about 8 months more would be great.