Unpopular opinion, I guess: I kinda prefer canon...ish... Felix over his concept self? Like, I honestly understand his PV version (F!Marinette was totally a villain to him and his plight with the ring), but... I'm not really into sad characters?
It just sorta fels depressing and I prefer when you don’t need to COUNT how many times the character smiled. Anyway, while I can understand the appeal of fanon Felix, he DOES feel too much cliche for me. Which is why I'm more into his canon self, make no mistake, he's still an ass, but he's the only CONSISTENT competent character, which I feel frutrated and like about.
For me, canon Felix is PV Felix, just brought to life and revealing some more aspects to him (like him doing magic tricks). Everything I've seen in canon Felix I have also seen in his older concepts. So to me, they are one and the same. We just have him brought into the show and getting expanded upon.
Canon Felix is a mischief maker who is spiteful to those who irritate him? So was PV Felix.
Canon Felix is a skilled actor and manipulator? So was PV Felix, coming forth to woo PV Ladybug and set himself up as smitten while secretly trying to get that kiss that would free him. Sidenote, both are also working off their own agenda and self-interests, especially as PV Felix wasn't being a true hero and went out for his own agenda.
Canon Felix is more of a solo show who struggles to make connections and is implied to be lonely? Same with PV Felix.
Canon Felix's design came out similar to Adrien? Well, that was one of the designs considered for him.
So with how canon has come forth with this character, from my perspective, this is the same Felix through and through. Even back in his concept days: he carried himself as someone who is poised, was a gremlin, spiteful, cunning, a skilled actor, and was here to work off his own agenda first and foremost. All of which is seen in both canon and concept. Canon has also oh so nicely confirmed my headcanon that when you are apart of his world, he will care greatly for you, as one of his reasons for getting the ring was for his mother, who he clearly loves.
Now fanon has done takes of him being sad or secretly soft or not really a spiteful mischief maker, kinda making him a more... dignified Adrien? Idk. Personally I've never seen Felix as a secretly sad character myself. Lonely and frustrated, I could see, but not so much sad. And that's a take that doesn't interest me as much either. It's one of the reasons I haven't found too many Felinette fics that grab me as they either go for him being "sad" or he is "softer" than he actually is, hardly ever causing chaos or mischief to others.
Since concepts to now, he's always been a dignified gremlin, and I rather this aspect of him embraced than softened or made to be "sad".