Of course, there are a whole series of other messengers that are all very similar in terms of their functionality, and also advertise secure communication through more or less complex encryption procedures.
We recommend the Threema service for the 4 messengers we tested, as it seems to offer the highest level of security in addition to convenient operation. Of course, the choice you make depends not only on the quality, but also on how many of your own contacts participate. Because if you have a very safe and comfortable messenger, but you stand alone with it, no one is served.
It is clear, however, that if you like messenger like WhatsApp belonging to a global corporation like Facebook through convenience gets bigger, and thus also makes a monopolist, this one eventually gives the carte blanche to do everything he wants.
Our recommendation is therefore to choose one of the safe and ad-free alternatives that is already used by your own contacts, or there is at least the willingness to change.