I'm firmly in the camp that it's not patriotic to stylize the American flag in any way... but I'd love it if you expanded on how this version is racist.
That would be true if they were actually using it to indicate support for police. But they're not. You'll only find it next to MAGA and expletive-laden flags.
Every time I've seen that flag, it's next to a Lets Go Brandon sticker or a Gadsden flag or similar. If I heard someone claim it was to show support for their local police department, I'd expect to see them smirking as they said that.
If that were true, it would have arisen spontaneously and not been rolled out as countermessaging to a protest movement about police violence.
No, this is 100% a political symbol with partisan (though not strictly party-aligned) intent, not a celebration of law enforcement. I don't think it's helpful to call it "racist", but neither is it appropriate to pretend that this isn't at least in some sense a "Fuck BLM" symbol either.
It can be a response to people taking a handful of incidents and ignoring the millions of safe and courteous police interactions a year. So while it may have been a response to cries about police violence, it doesn't automatically become some white supremacist pro police violence symbol....