I've only come close to multi-classing 3 times in 5e (so no, I have no MC 5e characters).
1) From an aborted campaign that began with Lost Mines I have a Human Fighter who has the Magic Initiate feat to represent him being partially possessed by a fire spirit. So for backstory & future RP considerations I limited him to "fire" effects. In the future I had planned to go Eldritch Knight.
I was also pondering MCing into Sorcerer or possibly Warlock as the spirit became stronger..
Alas, the game fell through before I hit 3rd lv.

But I've still got his sheet. So if I ever get to experience 5e again as a player I'm good to go.
2) There was one week during our CoS game where I had to seriously consider MCing my Warlock.
I picked up a magic staff and got possessed by the spirit of an evil wizard. As that items written? That's it. There's no becoming un-possessed & your personality shifts (and not for the better). And my patron would absolutely not continue granting me more Warlock powers. The next time I'd lv up it wouldn't be as a warlock. Or if I did it wouldn't be with my original patron. And Barovia isn't really the place you want to go shopping for a new patron.... So it was probably going to be wizard.
I would've become a Warlock 6/Wizard 1.
Fortunately the DM realized that, because I
would play that out, this would destroy everything about one of the best characters in his game & he let a series of Remove Curse & Banishment spells flush the evil spirit out of my warlock.
3) My Barbarian
almost MCd into fighter at lv.8
For a very brief moment the party had a Dragonborn Fighter (battlemaster). This rigid & highly disciplined DB was appalled by the halflings complete & utter lack of training. And astounded that none of the other characters had yet bothered to teach her how to fight properly! See, when forced to fight? The halfling didn't actually know what she was doing. She was scared to death & would randomly freak out (rage), swinging & hacking wildly. Anything & anyone in an adjacent square was a potential target. (all attacks when I raged were allocated randomly

)
Up to this point the party had learned to deal with this
BY NOT BEING ADJACENT TO THE HALFLING in a fight.
Wich did absolutely nothing to help her combat anxiety....
So the DB player & I role-played the Fighter beginning the barbarians "proper" training. With the end goal of me being a Barbarian 7/Fighter 1 the next time I lvd up.
Unfortunately the DB got disintegrated before we hit lv 8, couldn't be saved, & obviously didn't complete my training.
So we rolled an Int check vs a DC (I forget the target #) to see if the barbarian had learned enough to qualify as a fighter. She failed. So she lvd up to barbarian 8 & took the linguistics feat instead, learning enough D&D Egyptian/Arabic to decipher the assorted runes & hiroglyphs that played a large role in the campaign.
(Int is not her dump stat. She's quite intelligent, the d20 just wanted to roll low at the moment of leveling.)