Through the use of dragon balls, it is indeed possible for a human to achieve Ultra Instinct. Although only two wishes are needed for this to be possible, a third would certainly improve the chances.
So far, the imperfect form of Ultra Instinct has been used by Beerus, while the Grand Priest, Angels, Goku, and Moro utilize the perfect form of this technique.
So yes it is very much possible for an earthling to achieve Ultra Instinct, or at least something very similar.
As of the end of Dragon Ball Super, Goku is the only mortal to ever achieve Ultra Instinct and it seems he may hold the title indefinitely. As we have seen in Dragon Ball Super and Dragon Ball Resurrection F, the only other beings capable of achieving any mastery of Ultra Instinct have been gods.
Ultra Instinct is an ultimate technique that separates the consciousness from the body, allowing it to move and fight independent of a martial artist's thoughts and emotions. It is an extraordinarily difficult technique to master, even for the Hakaishin.
To unlock this, players need to finish PQ 154 (Dabura The Loyal? Servant), where players have to clear the mission in under 10-minutes, with players fighting the likes of Metal Cooler, Majin Buu, Super 17, Baby, and Omega Shenron.
Hercules is the Olympian God of Strength, and he might be one of the unique ones on this list capable enough of matching and overpowering Ultra Instinct Goku in terms of pure strength. Being a Half-God, Hercules is nigh-omnipotent and invulnerable to almost anything.
Through intense training, a human can, in theory, achieve Ultra Instinct form, managing to surpass Goku's Super Saiyan God form and gain power on par with the Gods of Destruction themselves.
1 Autonomous Ultra Instinct
Autonomous Ultra Instinct is an incredible transformation, allowing Goku to become a natural fighter whose instincts were honed to such a massive extent that he didn't even need to think twice before engaging in battle.
In summation
Through the use of dragon balls, it is indeed possible for a human to achieve Ultra Instinct. Although only two wishes are needed for this to be possible, a third would certainly improve the chances.
Ultra Instinct can only be activated at the brink of death. Ultra Instinct drains an insane amount of stamina and energy.
Through training, Goku developed the ability to utilize the Ultra Instinct Sign at will. Merus points out that at that point Goku was just one step away from achieving the full form and when he does he will be able to access it whenever he wants, and thanks to having become stronger, he will be able to keep it stable.
The in-story reason for this is provided in the Dragon Ball Super manga series. Speaking with Vegeta, Goku reveals that ever since the Tournament of Power ended, he's been unable to repeat his Ultra Instinct transformation, implying that the power can only be used in the direst of situations.
Same reason Goku as also not mastered it. Beerus simply hasn't reached that level yet. Although obviously Beerus is closer to Whis ability to use Ultra Instinct than Goku.
At this point in the anime, none of the three have been able to unlock a form possibly because humans simply don't possess the physical capability to pull it off. The same can be said for Tien, who isn't a human, but he is an Earthling.
Multiply that by 100 and Timeskip Base GT Goku would be 6400x stronger than Omega Shenron. With that amount of strength his power would be more comparable to MUI Moro arc Goku while only using SSJ.
According to Whis, it is possible for Goku to use Ultra Instinct without needing to transform, thus it will free him of the stamina drain that is creating a time limit while using it with a transformation.
Goku (Marvel) is the Alternate Dimension Counterpart of Son-Goku from the Dragon Ball Series. Like his Jump Manga Counterpart, he is indeed a Saiyan. He lives in a Different Dimension from the Canon Marvel World, somewhere in the MCU.
By using his Ultra Instinct -Sign- form, Goku achieved True Ultra Instinct, which affords him the benefits of Ultra Instinct along with the willpower gained through his Saiyan emotions and is Goku's strongest form to date.
It is very rare, and only obtained by consuming the Ultra Instinct scroll, which is dropped by the Ultra Instinct Karrot boss with a 0.1% drop rate.
While Perfected Ultra Instinct possesses incredulous power, its demand for calm and emotionless battle appears to stem directly from the nature of the Angels, who are even more aloof from things that would normally concern even Goku, such as the threat of a loved one or a planet being destroyed.
During Goku's battle with Jiren in the Tournament of Power, after Goku absorbed the energy of the Spiritbomb, the explosion of the Spiritbomb triggered Goku to be able to master Ultra Instinct temporarily.