No, it only updates one channel (root’s nixos channel), while --upgrade-all updates all of them. But yeah you need to be using 26.05, I missed the 25.11 mentioned there. Releases are in Year.Month format, and you had the month after that to upgrade. After July 2026, 25.11 was no longer supported.
Similar steps to below:
(But replace 24.11 with 26.05 obviously.)
And do not touch stateVersion in your config. Ever.