Depends on how dogmatic you want to get. Signal gets a passing grade from nearly all privacy focused groups, including the EFF.
Of course it has centralized control, and if they really wanted to, they could push out a change that creates huge privacy and security problems, but as a not for profit, they really have no incentive to do anything nefarious.
https://www.eff.org/deeplinks/2023/09/eff-award-winner-signal-foundation
If you truly want to have 100% security, you need to go to school for a decade, learn how the latest encryption and security works, create your own ecosystem, and have zero bugs or problems.