That link, and I could be missing it, has nothing to do with what I claimed. Mind editing your post and quoting a red flag linked at the source you provided?
Some of my favourite red flags:
Signal’s dependence on Google libraries: https://github.com/signalapp/Signal-Android/issues/9044#issuecomment-535194837
Signal dev bullshitting a non-answer and then hilariously refuting his non-answer: https://github.com/signalapp/Signal-Android/issues/9044#issuecomment-534340623
Signal hiding its serverside source code for many months: https://github.com/signalapp/Signal-Android/issues/11101
You can find many more examples.
The last one about server side code, together with Signal’s funding sources and their obsession with phone numbers code leads me to suspect that Signal is just a honeypot by US intelligence.
Those clients exist despite Signal Foundation, not because they encourage community development. They are doing everything they can to discourage third party app development.
That was your original claim. None of the sources you provided back up your original claim. We can talk about Google libraries or the delay in server side code if you want to go down that path, but that’s a completely different discussion. Why are you pivoting to other topics? Will you concede your original point or do you have evidence to back it up?