I have been considering this question too, since I've relied on Ubuntu for awhile. I hate to say it, but I've come to think that Gentoo or Guix may be the only reasonable options right now. I say "I hate to say it" because both are supposedly quite difficult to set up and administer compared to a distribution like Ubuntu. I have not used either so cannot speak from experience, only from what I've read.
I considered Debian for awhile, in part because it's familiar and relatively easy. However, as an outsider to that project I'm concerned about some of their internal discussions concerning AI. It wouldn't surprise me if they eventually decided to accept AI-generated code submissions in certain cases, or allow AI to "review" things. Once that crack opens a flood follows, if experience is any guide.
I'm of a mind that as annoying as it can be, compiling your basic tools from source code that you can peg to a specific version (pre-AI-slop-contributions) is the only way to really avoid AI at the OS level. This situation cries out for a community "No AI" distribution, frankly, but I haven't seen anything along those lines yet (such things might exist but I don't track all this that closely)