XMPP server is slightly easier to setup and it requires far less resources than matrix. I think that in the server aspect XMPP is superior, in both performance and scalability (ejabberd).
The client setup in XMPP and Matrix seem to have the same usual steps (username and password). No big differences here, other than Element defaults to matrix.org to create an account (which contributes to centralization).
I'd say that XMPP clients are generally better than matrix's ones. Maybe because matrix is an immature and younger protocol, but Element seems to be the only client that implements everything and UI is confusing and it's electron.
And a personal preference, I like using my GPG keys to encrypt my conversations when possible in XMPP. This wouldn't be possible in matrix.
Even better: instead of desperately patching Microsoft's crap, move to an OS that won't remove features and where you could write your own features if you wanted to.
A 2009 thinkpad is rather capable of being a daily driver for most people. Saying otherwise, you're only contributing to the growing problem of ewaste.
Even the T60 offers a decent performance if your usecase is browsing the web, mail and other simple tasks.
The FSF might be wrong in some aspects but there's no real alternative to Libreboot. The Framework laptop is not free software friendly. Even if it was corebooted, it would require many proprietary blobs and it's highly unlikely, if not impossible, that they will be ever able to remove the Intel ME.
There are other options that are nearer to be completely free (as in freedom) hardware, eg the Pinebook Pro. I'm unsure if there are any proprietary blobs required to boot it tho, but the lack of Intel ME makes it a much better candidate for a new generation of 'libre' hardware.
But yeah, I agree. We need a feature phone with IM support. That would be perfect.