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Best FOSS Local Messenger Service?
(beehaw.org)
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
Its not strictly needed but everything is build with that assumption in mind and thus there will be many papercuts.
Yes you can self-host Element, but you have to be very careful with the setup to avoid cors issues and I think it will also permanently show a big warning if the connection is not via HTTPS.
Bottom line, it can work, if matrix is what op wants to go with.
As for SLL, without it any browser based thing is going to get you a warning, from the browser itself, at least.