"(S)imba and the other called (K)imba"
Kimba is a localised name. His name is Leo in the original work, which is titled 'Jungle Emperor'. Simba literally means 'lion' in Swahili, which is consistent with all the names in The Lion King.
"both characters have a talking bird as sidekicks"
Zazu isn't a sidekick. He's more like a royal guide/caretaker. Other than being birds and having a similarity with tempers (though nowhere to the same degree), they have nothing in common.
"both had their father killed when they were cubs"
Oh, and did Simba also have several scenes where he dragged his dead father's corpse around?
"both of them talked to their dead father in a vision on the clouds"
Yeah, that's not even close to true. Kimba not only didn't talk to the cloud, but the cloud was actually Kimba at the end of the series, after he *spoiler alert* dies.
"And both shows feature a black haired lion with a scar in its left eye as a villain (with a group of hyenas as henchmen)"
Outside of being very common tropes, the lion and hyenas in Kimba are not only not the primary antagonists, they only actually show up in a handful of episodes (out of hundreds). So unimportant, they weren't even included in the compilation movies for the series.
I'm not gonna watch the video you're sharing, but I'd venture to guess at least 90% of the footage it shows, is from the Jungle King Leo movie which released 3 years AFTER The Lion King, and all the comparitive shots from that movie were never in the Kimba source material.
Even if some of it was inspired by Kimba, they'd have no reason to lie about it as the similarities are very superficial at best. Not including the more similar shots from the 1997 movie of Kimba, 3 years after The Lion King.
And if you're gonna point out superficial similarities, then there's basically nothing in the continent of Africa Disney could've used, that wasn't in one of Kimba's random episodes. Which is when it falls into the 'Simpsons did it' dilemma.
Go watch the YMS video that was already shared in this thread. It's two and a half hours, but it's a lot shorter than having to watch all of Kimba, and is far more well sourced and comprehensive than anything else on youtube.
If you can't be bothered to do that, then don't waste people's time by repeating these fallacies.