You should definitely use open-source, encrypted messengers such as Briar, Signal, Threema, Element or SimpleX. Avoid insecure commercial messengers such as WhatsApp and co.
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If you are unsure which messengers are good or if you need arguments to convince family and friends, you should definitely take a look at Kuketz's messenger matrix. There you can easily compare the individual messengers according to functions and security aspects. Also bear in mind that the police in some countries already operate chat apps themselves to make it easier to obtain investigation data.