I will be arriving at Munich Airport Terminal 1 on an international flight at 7:45 PM, and my next flight to Berlin is at 9:45 PM from Terminal 2. I will be holding two separate tickets (Oman Air and Lufthansa). Is the transit time enough? I would appreciate any advice.
Munchen airport is relatively small and it has no common transfer zone between two terminals.
For you it means that you must pass the border during arrival. It will takes a time (it depends of amount of passangers). Say at least 20 minutes on arriving. Don't forget about queues on departure - 10 minutes (it's always full of people).
Also since you fly by different airlines you should get your baggage after arriving to Munchen. Usually it takes 20-30 minutes.
Plus 10 minutes walk between terminals
In a best scenario you will be in Terminal 2 at 8:45 PM
By rules of Munchen ariport you should check in with baggage not later than 40 minutes before departure.
So you have about 20 minutes on emergency case. I think it's enough.
We already have questions about transfers in Munich, e.g. Is 1½ hours enough for a transit at Munich airport? Your situation is different because you have separate tickets but the answers seem encouraging. It's always risky especially if you have a long-haul flight in the mix and can't count on the airline's assistance. 2 hours is very short in any case but if there is a place where it can work, it seems to be Munich.
It might turn out to be costly but Munich is not far from Berlin and well connected to it so in the worse case finding another flight or even a train should not be an issue. I think you would have to wait for the next morning, though. If you can still do something about it, I would therefore try to get a better connection.
Also, do try to get your luggage checked through to your final destination. Oman Air does list Lufthansa as an Interline partner and it might be possible even if you have separate reservations. If you manage to do that, you would save some time in Munich and avoid the whole waiting for luggage/luggage drop deadline issue so that you could still make it if your incoming flight suffers a moderate delay.