(Note: I didn't test the changes as I don't use this program anymore.)

Did you find a better alternative for your needs?

The default package should perhaps be set to taskwarrior3 for stateVersions more recent than the current stable?

Users not already on taskwarrior3 receive the following warning:

trace: evaluation warning: taskwarrior was replaced by taskwarrior3, which requires manual transition from taskwarrior 2.6, read upstram's docs: https://taskwarrior.org/docs/upgrade-3/

Avoiding the breaking change of setting pkgs.taskwarrior3 as the new default aligns with the approach in NixOS/nixpkgs#303632. Until Nixpkgs hard deprecates taskwarrior2, we should follow their approach.

This would be more consistent with what is being tested in the module test too.

Are you referring to the following:

diff --git a/tests/modules/programs/taskwarrior/taskwarrior.nix b/tests/modules/programs/taskwarrior/taskwarrior.nix
index f21198f5732b..ea6cde3a1316 100644
--- a/tests/modules/programs/taskwarrior/taskwarrior.nix
+++ b/tests/modules/programs/taskwarrior/taskwarrior.nix
@@ -16,6 +16,7 @@ with lib;
         include /my/stuff
         urgency.user.tag.test.coefficient=-42.42
       '';
+      package = pkgs.taskwarrior3;
     };

     test.stubs.taskwarrior = { };

I added this to verify that pkgs.taskwarrior3 still exists if it ever gets replaced with pkgs.taskwarrior in the future. This makes it easier to spot when to partially revert this patch.

LGTM, I agree with following the nixpkgs approach.

I am not sure if setting a taskwarrior3 in the test is a good idea. In my opinion, it's better to ensure that the default option is valid than checking that the example option is.

This other PR has been merged and covers the taskwarrior-sync part: #5802

Thanks! I've adjusted for the previously merged taskwarrior-sync PR and merged this PR to master now 🙂