@raketenlurch thanks for mentioning three solutions at once:
- #Element https://element.io
- #Signal https://signal.org
- #XMPP https://xmpp.org
From this poll, friends recommended many XMPP apps such as #Blabber (https://blabber.im/en) and @kaidan (https://kaidan.im). Honestly, I also interested in #Movim (https://movim.eu) as it has video call I heard.