Would simple secure apps such as "Signal and WhatsApp" or similar defeat eavesdropping on mobile phone conversations by state actors?

There are various situations where adversarial security services are trying to eavesdrop and listen in on mobile phone conversations such as here on this thread

>Russia may have attempted to scoop up the Ukrainians' mobile phone data with special telecommunications equipment, using a device such as a stingray.
>
>[https://www.reddit.com/r/ukraine/comments/wy7k92/russia\_spied\_on\_ukrainians\_training\_in\_germany/](https://www.reddit.com/r/ukraine/comments/wy7k92/russia_spied_on_ukrainians_training_in_germany/)

Would a simple and guaranteed solution to prevent eavesdropping from any adversary be to just install Signal/WhatsApp or similar and speak via that - Could this be a simple 100% …

apps eavesdropping mobile phone privacy signal simple state whatsapp