Signal is only Open source by name, as they don't authorize anyone to make their own clients. FOSS is about power to the end users, and Signal is fighting hard against it.
Being OSS doesn't mean they have to be fully transparent on their plans, nor does it mean they have to cave to abusive behavior in PRs, feature requests or forums.
Nobody has to be "authorized" to do anything with code shared. That's not how the licenses work.
> FOSS is about power to the end users, and Signal is fighting hard against it.
"power" here means the ability to derive your own forks (see https://github.com/dennisameling/Signal-Desktop).
Being OSS doesn't mean they have to be fully transparent on their plans, nor does it mean they have to cave to abusive behavior in PRs, feature requests or forums.