If we're talking about mobile apps only then ntfy, Fluffy Chat, KDE Connect, Nextcloud, Tuta, Protonmail, Session, Conversations, Organic Maps, Fedilab, Mull, DAVx and KeePassDX.
I am on a grandfathered Tuta plan that costs me about $2 CAD a month. I also pay for Proton's premium plan. Both are worth it to me. I get that everybody has a budget but at the same time 10 Euros a year is a tight one when dealing with privacy friendly alternatives.
I use the TOTP option in KeePassXC and KeePassDX to handle 2FA duties. I backup the encrypted file to my Nextcloud. If you self host Nextcloud or something similar this is a viable option.
I have gotten tech minded friends to switch with some success. Getting my wife to switch to privacy friendly communications with me was easy in that I did all of the leg work. I setup her accounts and installed the apps. As far as she was concerned the phone came with XMPP, Matrix and Tuta.
I have switched my comunications to anything else. XMPP, Matrix, Session, Jami, etc. I text as little as I can. No matter the app the messages still go to my carrier.
Neither really. Telegram is closed source on the servers and is known to cooperate with governments and law enforcement. Signal is the better option but I refuse to use an app that requires my phone number when alternatives like Matrix; XMPP; and Session exist. My phone number is tied to my name; address; and payment methods. It's not a small ask of Signal in my opinion.
I already use Trisquel; libre kernel; Abrowser; DivestOS; SearXNG; Nextcloud; Matrix; XMPP; Session; Odysee and Peertube; KeePassXC; Tutanota and Protonmail; ProtonVPN. Not sure How much further I can go without going with a Talos II.
If we're talking about mobile apps only then ntfy, Fluffy Chat, KDE Connect, Nextcloud, Tuta, Protonmail, Session, Conversations, Organic Maps, Fedilab, Mull, DAVx and KeePassDX.