Ultimately you will have to make some concessions in regards to privacy. Most people aren’t going to install Signal just to talk to you because it does not fit their use case.
I’m also gen z and from the US, I go to university, and most people who I know use Whatsapp or Discord to communicate. While Whatsapp is not perfect, their messages are end-to-end encrypted, which is much better than most other mainstream platforms (I would honestly say that it is better than Telegram). Discord can at least be accessed through a browser with an email alias.
My preference for communication would be:
Best realistic case: Whatsapp or iMessage (if you have an Apple device)
Reluctantly use: Discord, Instagram, Telegram, SMS, any messenger that can be accessed through the browser without installing an app