- `boot.kernel.sysctl."net.core.wmem_max"` changed from a string to an integer because of the addition of a custom merge option (taking the highest value defined to avoid conflicts between 2 services trying to set that value), just as `boot.kernel.sysctl."net.core.rmem_max"` since 22.11.

- `boot.loader.systemd-boot.xbootldrMountPoint` is a new option for setting up a separate [XBOOTLDR partition](https://uapi-group.org/specifications/specs/boot_loader_specification/) to store boot files. Useful on systems with a small EFI System partition that cannot be easily repartitioned.

- `boot.loader.systemd-boot` will now verify that `efiSysMountPoint` (and `xbootldrMountPoint` if configured) are mounted partitions.

- `buildDubPackage` can now be used to build Programs written in [D](https://dlang.org/) using the `dub` build system and package manager.
  See the [D section](https://nixos.org/manual/nixpkgs/unstable#dlang) in the manual for more information.

- `castopod` has some migration actions to be taken in case of a S3 setup. Some new features may also need some manual migration actions. See [https://code.castopod.org/adaures/castopod/-/releases](https://code.castopod.org/adaures/castopod/-/releases) for more information.

- `documentation.man.mandoc` now, by default, uses `MANPATH` to set the directories where mandoc will search for manual pages.
  This enables mandoc to find manual pages in Nix profiles. To set the manual search paths via the `mandoc.conf` configuration file like before, use `documentation.man.mandoc.settings.manpath` instead.

- `drbd` out-of-tree Linux kernel driver has been added in version 9.2.7. With it the DRBD 9.x features can be used instead of the 8.x features provided by the 8.4.11 in-tree driver.

- `garage` has been updated to v1.x.x. Users should read the [upstream release notes](https://git.deuxfleurs.fr/Deuxfleurs/garage/releases/tag/v1.0.0) and follow the documentation when changing over their `services.garage.package` and performing this manual upgrade.

- `hardware.pulseaudio` module now sets permissions of pulse user home directory to 755 when running in systemWide mode. It fixes [issue 114399](https://github.com/NixOS/nixpkgs/issues/114399).

- `kavita` has been updated to 0.8.0, requiring a manual forced library scan on all libraries for migration. Refer to upstream's [release notes](https://github.com/Kareadita/Kavita/releases/tag/v0.8.0) for details.

- `krb5` module has been rewritten and moved to `security.krb5`, moving all options but `security.krb5.enable` and `security.krb5.package` into `security.krb5.settings`.

- `libass` now uses the native CoreText backend on Darwin, which may fix subtitle rendering issues with `mpv`, `ffmpeg`, etc.

- `libjxl` version was bumped from 0.8.2 to 0.9.1 [dropped support for the butteraugli API](https://github.com/libjxl/libjxl/pull/2576). You will no longer be able to set `enableButteraugli` on `libaom`.

- [`lilypond`](https://lilypond.org/index.html) and [`denemo`](https://www.denemo.org) are now compiled with Guile 3.0.

- `lxd` has been upgraded to v5.21.x, an LTS release. The LTS release is now the only supported LXD release. Users are encouraged to [migrate to Incus](https://linuxcontainers.org/incus/docs/main/howto/server_migrate_lxd/) for better support on NixOS.

- [`matrix-synapse`](https://element-hq.github.io/synapse/) homeserver module now supports configuring UNIX domain socket [`listeners`](#opt-services.matrix-synapse.settings.listeners) through the `path` option.
  The default replication worker on the main instance has been migrated away from TCP sockets to UNIX domain sockets.

- `mockgen` has changed to the [go.uber.org/mock](https://github.com/uber-go/mock) fork because [the original repository is no longer maintained](https://github.com/golang/mock#gomock).

- `mpich` now requires `withPm` to be a list, e.g. `"hydra:gforker"` becomes `[ "hydra" "gforker" ]`.

- `nextcloud-setup.service` no longer changes the group of each file and directory inside `/var/lib/nextcloud/{config,data,store-apps}` if one of these directories has the wrong owner group. This was part of transitioning the group used for `/var/lib/nextcloud`, but isn't necessary anymore.