I only have a few privacy-focused friends on Signal and Matrix and I talk to them that way. I have a few friends who use my personal Nextcloud and just use Nextcloud Talk to chat with me. For all others, I still use the mainstream platforms and just take care to not post any info that I don’t want public and I make sure the apps have limited info and app permissions.
I think it is tough to convince others to switch until they themselves see the need, at which point they’ll start asking you for advice on what to do.
With new contacts, I’ll usually ask if they have Signal first and if they don’t then I don’t really push it. I think just getting the name out there every once in a while is the most you can do.
I would not recommend going to the open ones just yet. There are major performance issues with the GSP firmware. You can disable it on the proprietary modules but you can not do so on the open modules since they rely on it for functionality.