The only really secure messenger is Matrix, but it is quite unusable.
The best client i have found is FluffyChat which is at least on par with WhatsApp all considered.
Sadly Telegram has by far the best UI, UX and Dev UX there is of all messengers, which is why i like to use it, also it is fast as heck.
@m you might want to double check on Matrix though:
https://soatok.blog/2024/08/14/security-issues-in-matrixs-olm-library/
Matrix is a decent IRC replacement, but a secure messenger it is not. I've always felt that encryption was bolted-on as an afterthought in it and that that will lead to tears, and as time goes by I get more and more proof of this.