There is very little correlation between being likable and unlikable and being good or evil.
Many people become disgusted by other persons when they discover that those other persons are evil. Once they discover those other people do evil deeds, they can no longer like them.
So there is some correlation between how good or evil someone is and how likeable other people consider them to be. But I am sadly disappointed in the human race, considering how little correlation there is.
Think about the usual list of the most evil persons in history, who massacred the most millions of men, and women, and children: Genghis Khan, Tamerlane, Hitler, stalin, and Mao.
Anyone who can't ignore how evil someone is, or can't force themselves to like someone who is evil, could never like Genghis Khan, Tamerlane, Hitler, stalin, or Chairman Mao. But on the other hand, many people who knew them personally considered them to be people with combinations of attractive and annoying personality traits, like everyone else they knew. They didn't seem instantly unlikable to everyone they met personally, despite being so exceptionally evil.
In my own experience in junior high school and high school, most of the boys were bullies to a greater and lesser degree, and at least 10 percent of the boys in my class were bullied more or less often.
And maybe bullying is not a very strong evil and doesn't have a very high evilness quotent. But the evilness of bullying is very pure. Nobody gains anything from bullying, like a counterfeiter or a bank robber might gain from their crimes. bullies eem to bully to get pleasure from the suffering of the bullied. So bullies seem to be doing it for what TV Tropes calls "for the Evulz", out of pure evil.
https://tvtropes.org/pmwiki/pmwiki.php/Main/ForTheEvulz[1]
And in my experience the majority of high school boys are at least occassionally bullies.
And from what I have heard the majority of high school girls are also at least occassionally bullies, though typically with a different style than boy bullies.
So a large percentage, probably a majority, of high school students at least sometimes commit acts of pure evil. But a large percentabe, probably a majority, of high school students are somewhat likeable and are liked by a number of other stundents and adults who know them. And it seems statistically very likely that those two very large groups of high school students have a considerable degree of overlap, that many high school students who bully are also likeable to some people, if not to those they bully.
In the Get Smart televison series (1965-1970) the spy organization Control fought agains the evil spy organization KAOS. In the episodoes "And Baby Makes Four" and "And Baby Makes Four, conclusion", Simon the lIkeable was a totally charming and likeable evil KAOS agent.
KAOS's "most irresistible agent". As the Chief explains it, "a man so unassuming, so modest, so sweet and warm that you take one look at him, and you like him."
Nonetheless, Simon the Likeable remains capable of all the wicked and evil acts that one expects of a KAOS agent, for instance freely admitting in a London court to grand larceny, forgery, espionage, extortion, counterfeiting, smuggling, and assault with a deadly weapon. Yet, to the cheering of onlookers, the Lord Justice on the case takes a look at him... and dreamily finds him "Not Guilty!"
https://getsmart.fandom.com/wiki/Simon_the_Likeable[2]
TV Tropes has a supertrope Likeable Villian, which includes many tropes about ways in which various villains are more or less likeable.
https://tvtropes.org/pmwiki/pmwiki.php/Main/LikableVillain[3]
No doubt the examples they list will include many characters you are familiar with.
And you should see the trope Designated Hero
A Designated Hero is a character who, despite being presented as The Hero within a story, doesn't really do anything heroic. Viewers may typically see this character as a Jerkass and, at worst, a villain. This is not the same as the deliberately morally ambiguous Anti-Hero. From the praise Designated Heroes receive from other characters, the narrative, and perhaps Word of God, it is plain that the audience is expected to like and root for them. Instead, many viewers have trouble liking the character and may even feel disgusted by them.
https://tvtropes.org/pmwiki/pmwiki.php/Main/DesignatedHero[4]
It has many examples of characters who the writers make the protagonists who do evil deeds.
So there are many examples of fictional caracters who are more or less evil and and more or less likeable.
As for evil scientists, in real life most evil scientists and engineers are those who work for their national governments to develop weapons of war, not sterotypical fictional mad scientists.
As for fictional mad scientists like you intend your character to be, perhaps you might go back to the prototype story with a mad scientist main character - Frankenstein, or, The Modern Prometheus, by Mary shelley, 1818. Victor Frankenstein has a number of character flaws, but he creates his monster in an attempt to better humanity.
So it seems to me that it is perfectly possible to create a mad scientist character who is the hero of the story, whose project will benefit humanity, and who is competent enough to carry it out successfully.
And if it is posible to do that, it would be possible to created a mad scientist character who was evil, but had likeable characteristics.
