I don't know, it's true but I'm not concerned with what the TVA knows now under Kang's rule, I'm concerned with why they didn't know about it under HWR rule. Remember HWR wasn't concerned with branches specifically, he was concerned with branches that could lead to Kang. If there were methods of time travel that could lead to Kang without creating branches that's something HWR would prevent through the TVA. That's why it makes sense that Kang is the only one who can do it. Like you said, the TVA knows what HWR tells them about time travel, so if they needed to be aware of it they would be. But if the secret of branches time travel remains only with variants of Kang like HWR, of which he's the only one, then they wouldn't need to be aware.
If Kang is the only one who can change events without creating branches then the TVA doesn't need to know cause Kang doesn't exist except for HWR, thanks to HWR. If other people can do it then they'd need to know to effectively stop Kang's from potentially appearing. If branchless time travel was possible before Loki we'd know about it. There's a reason Kamala could do it and there's a reason the TVA doesn't know about it (unless Marvel just really doesn't care about that inconsistency which I doubt). This explains both.
TL;DR if Kang and his tech are the only ones that can time travel without branches and HWR is the only variant of them that's time travelling until his death then the TVA doesn't need to know. If the Bangle is Kang tech as the design seems to imply then this explains A. why Kang is such a threat to time B. why Kamala can perform branchless time travel and C. why the TVA (and by extension the audience as they're the way we were informed of the rules largely after Endgame) was kept unaware of it cause they didn't need to know.