Is it a pattern that every time a movie, show or animation that doesn't have a white person as the protagonist is attacked by right-wingers?

It's real. Conservatives are awful people.

"Political Correctness", "Social Justice Warrior", "Woke", "Diversity, Equality, Inclusivity"; the shit-for-brains bigots will always try to make their hatred seem reasonable and just. Don't be fooled!

It's real, but you don't get to see anything from billions of viewers who don't mind or even enjoy a little variety. Only the five hillbilly snowflakes who feel offended by a skin tone bother to voice their stupid opinion.

With the low level of detail that's used for most anime faces and the wild (by Japanese standards, anyway) hair colors, it's usually pretty much impossible to tell without context whether a character is meant to be asian or european.

On a more ideological level, Japan was allied with Nazi Germany and committed a lot of atrocities back then, and they always had strong anti-immigration policies and an advantageous position to enforce them (island nation, difficult writing system etc.).

Yes

Aggrievement is the central tenet of these people. They imagine it everywhere and never accept reality.

Yes, and you'll be "woke" for liking something without a white main character. Part of their playbook. Can't just be happy for someone else making it.

Every single right leaning person I know LOVES several movies and shows that have main characters that aren't white men.

The boondocks, blade series, basically anything Morgan Freeman or Samuel L Jackson have done, Lando, Morpheus and uncle Phil off the top of my head.

I am aware there are the super racist far right guys that probably can't even watch Scooby Doo because the dog is brown, but the grand majority of "right wing" people aren't white supremacists that lose their shit if a character isn't white in their movies and shows. Even if that's what some people here might tell you is the case.

I think people have complained about casting choices forever. The first female Hamlet must have gotten some negative press as well. I believe the pattern you see is based on two factors:

1. We all carry a media device with us. We are quick to respond and post stuff publicly and in return we get to read other people's thoughts. What would've taken a couple of weeks to spread to enough people to make a dent in any poll in the age of newspapers can take a day or so now. So the speed has picked up. Also, the stuff our media devices serve us depend to varying extents on the use of algorithms. We know that especially in the realm of social media, user engagement is strongest with stuff that riles us up. So the old algo serves us more of that. Algorithms distort the picture. Things are labeled as viral when they are viewed by thousands of people - on a planet of 7 billion or thereabouts. Storms on the internet tend to be teacup size most of the time. The internet gives us a distorted picture where a small number of people can pretend to be a significant portion of society. And that doesn't mean the Illuminati control this sinisterly; it can just be a few d-heads who think alike that start stirring the teacup. But PR agencies exist to make use of this as well.
2. Politics and society are not on a linear trajectory to paradise. While overall we're better off as a species than 1,000 years ago, the way stuff moves is often 3 steps forward and 2 steps back. One could say, the US (as one example of many countries today) has just taken two steps back. A political movement that we thought was done for after we have all seen where it can lead is back: right-wing populism. It is a backlash to well intentioned political decisions with regard to equality, the eradication of racism, allowing women autonomy over their own bodies, etc. A lot of people had differing opinions about these things but social norms had confined them to family gatherings and the pub where they could voice them but not much more than that. Now they can voice them online as well and find many other dissenters they wouldn't have found as easily just 30 years ago. And because they feel like a majority (see 1)) or a significant portion at the very least they become more outspoken. Saying the quiet parts out loud. So talking badly about people of another ethnicity, women, etc. is en vogue again. So any opportunity for that is good enough.

So Star Wars is casting a non-binary person to lead a new show? "Fans are outraged!" The new 007 is a black woman? "Fans are up in arms!" These have become predictable reactions that gain traction in for-profit media that also needs us to engage so they can sell ads. So is this a pattern? Yes. Is it new though? I don't think so. It's just accelerated, amplified, fueled by politics, and more often than not a storm in a teacup.

Before I finish this essay, I would like to point out two examples that popped into my head that go against the grain. Scarlet Johansson's casting in Ghost in the Shell caused a stir. And about a decade earlier Benedict Cumberbatch as Khan from Star Trek was also met with criticism.

For every single piece of corporate media, you can find someone on the internet saying something bad about it.

Different aspects will invite different types of people.

For example, casting a non-white person as Snow white, that'll invite everyone with a pair of eyes to ask why? Or for another example, giving Lara Croft smaller boobs will invite the gooners to say something. Modern Star Trek will invite old trek fans. I can go on.

Most corporate media these days is made by lefty companies like Disney, so you'll see more of those kinds of criticism.

Whether or not it's legitimate criticism is up to you though.

"Every time" is certainly an exaggeration. Just off the top of my head in a minute:

• The Dragon Prince - nobody gave a damn.
• Star Wars [pick any of several releases] - we've had various people of color, both human and alien, as protagonists. I don't remember much of a fuss over that in particular.
• Various MCU things - Brave New World just came out, again featuring Mackie as Wilson - taking the place of the stereotypically WASP Steve Rogers, no less.
• Hazbin Hotel: Vaggie is heavily coded as latina.
• Mobile Suit Gundam: Witch From Mercury - okay, not a non-white lead, but the first Gundam series with a female lead, and a lesbian romance front and center. Once again, no attack.

If I looked around further, I'm sure I could find more. All of these have variously been critiqued for writing, characterization, or pacing, but failed to draw attacks based on the ethnicity (or orientation) of their protagonists.

Is this kind of attack a thing that happens? Absolutely. Is it "every time"? No. I'd suggest it's more often when a series goes out of its way to bludgeon the audience with a message related to it, or tries to sell a newcomer as a superior replacement for a legacy character, that people can get riled up.

No one cares who the lead is in a good show. It's been popular to blame racism/sexism for shitty shows for a while. It's easy to find a couple tweets and turn a handful of assholes into the face of criticism.