Here’s the thing, I love Autobot Megatron, I love his change of heart, his very real attempts to reconnect with the person he used to be. But if he really wants to be a changed bot, he’s got to deal with what he’s done to starscream. That 4 million year long toxic and downright abusive relationship between the master and his backstabbing second has been our up close and personal look at how much of a monster Megatron really was. The 4 million year war, the countless planets crushed beneath the decepticons heels are an abstraction at best for us.
Megatron: Spotlight had all the things that made Megatron an awful person on display- his brutality, hypocrisy (blame star scream for the state of the army when he were the one that wanted all resources devoted to rebuilding his body), the glee he took in the suffering of others, his selfishness, his cruelty, his sociopathy (abusing Starscream was ‘sport’). All of those things were directed at one person - Starscream. He bore the brunt of everything that made Megatron a monster right in the face. It’s not an accident that Starscream is a deeply paranoid and guarded individual who can’t even conceive of trusting anyone on a personal level.
If Megatron really wants to do a full on Heelturn, he has to apologize to Starscream, even if the act if futile, even if Starscream scoffs and mocks him, it doesn’t matter. He’s got to do it. Denouncing the DJD was a good start, they were the physical embodiments of his old self. Megatron needs to leave his dignity at the door and apologive for being absolutely awful to the backstabbing conniving bot that was trying to usurp him for eons. Starscream’s motives/behavior don’t change the fact that Megs kept him around as his whipping boy.
TL:DR; If Autobot Megatron really wants to put the past behind him, he has to deal with his twisted relationship with his second in command before he can move on.