Qfyilyi

I learnt from this question that Dormammu is a being who lives beyond time.

Generally, when you reverse time, you reverse everything including the
memory of the person existing inside the time. Since Dormammu doesn't
exist in the time, his memory does not get reset, therefore he gets
tired of seeing repeated thing for many times and is defeated.

Hence he knows what is happening around him and that he's locked in a time loop. If Dormammu could acquire the Time Stone by force, he could have broken the time loop. Since he knows that Dr Strange has set a time loop, why did he not attempt to steal the Time Stone instead of trying to kill Dr Strange?

Dormammu knew that Dr Strange had trapped him in a time loop, but he didn't know how. All Strange told him was:

Doctor Strange: Just as you gave Kaecilius powers from your dimension, I've brought a little power from mine. This is time. An endless looped time.

If the time loop had continued, Dormammu probably would have realised eventually that the glowing green amulet around Dr Strange's neck had something to do with it, but even if he were to steal it, he'd face two more problems:

1. It's unlikely he'd know how to use the Time Stone, given that he has no concept of time.


2. Each loop only lasted about thirty seconds. Factor in the time it would take him to steal the stone from Strange, who's not going to give it up easily, and he'd have a very narrow window in which to break the loop before time looped again and Time Stone was back in Strange's possession.

The key point, though, is that Dormammu didn't try and steal the Time Stone because, to the best of my knowledge, he didn't know about it.

Your question implies Dormammu can use the Time Stone, which is not necessarily the case.
Dormammu probably didn't try to get the Time Stone because he would have been unable to use it to break the time loop on his own. This could be explained by the Book of Cagliostro, as Dormammu did not read it.
(This is just my theory though.)

I'll try my best to stick to the MCU.

Please note that Dormammu is introduced as an entity beyond time, it means he is unaffected and above the concept of time, time has no meaning for him, hence his dark powers enable his minions to live forever, viz serve him forever.

Please note that it took a very good photographic memory,over-eagerness for Dr. Strange to know about the Time Stone-using techniques, his eagerness almost led him to get caught in a time loop (The eaten apple scene in Doctor Strange).

On the other hand, we have nothing in favour of Dormammu, he is unaware of time related concepts, so using the time stone as per his will is out of context when referring to Dormammu.

Mystically, he over-powered Strange quit easily, his physical significance and capabilities aren't disclosed in the MCU, so to win over Dormammu, being able to use time stone provided the edge for Dr. Strange.