This is really disingenuous coming from Signal who pioneered secure compute architecture for a number of useful features [1][2]. On-device checks are no more "surveillance" than Signal's private contact discovery is, and the same slippery slope argument applies there.
It's also technically incoherent: the exact same kind of "surveillance" is already applied by every single phone, because that's how the Photos app (or whatever it's called on Android) searches for cat pictures based on the text "cat". I can't recall any Signal statements about cat recognition technology leading to "reporting people to government authorities".
The "cover-ups" link right in the beginning is a real mask-off moment though. This is not a measured statement informed by the reality of modern Britain. It's an American view informed by the twitter cesspool and divisive rhetoric of the far right. It's a real shame to see Signal falling so low.