[tlu] Unable to find a valid update server.

[Karl Berry]

    Subject: [tlu] Unable to find a valid update server.

Maybe you are on an oldish Mac and you don't have any system curl or
wget available? The wget.x86_64-darwinlegacy binary supplied with TL
does not support SSL, and that is required now by the default repository
url, the https://mirror.ctan.org multiplexor.

So ... if this may be the case, you might try explicitly specifying an
http (not https) mirror from the list at
https://ctan.org/mirrors/mirmon.  Not an easy thing to search for, I
know, but that's where we are at the moment.

Adam: I'm afraid this manual selection of an http mirror is going to be
the only way forward for people on old Macs without an ssl-enabled curl
or wget available on their system. Norbert and I are cooking up some
tests to output a message in this case, but we can't feasibly
auto-choose an http mirror.

At least this is my current understanding of the situation.

Best,
Karl