I’m the project lead for Matrix (and Riot) and can categorically state we are not using user data for profit on Riot, and never will. The Riot privacy policy is indeed too heavy and scary atm but it boils down to “we collect information required to actually power communication; we don’t allow illegality or abuse; we keep the option to use analytics to see what features of Riot people use and so how to focus our dev effort”, which seems pretty reasonable to me. It also applies only to the default matrix dot org homeserver; if you use a different one (eg a hypothetical Purism one) then it can have whatever privacy policy it likes. More info over at About matrix and riot.
Personally, I rate the freedom to select and trust your preferred service provider as high as the need for privacy, which is why Matrix exists (rather than just using Signal). But OWS release a Signal app for the Librem5 you are of course welcome to use it. (Whereas with Matrix you are not beholden to OWS choosing to release an app for the platform).