Upgrading to 1.4.1
Version 1.4.1 is a bugfix release.
You can safely update the Hyva_Theme module (package hyva-themes/magento2-theme-module) to the latest version, even if you don't update the Default Theme to 1.4.1.
Backward incompatible changes
The Recently Viewed Products slider now uses CSS SnapSlider. If your customized Magento_Catalog::product/widget/viewed/list.phtml template references old JavaScript, it may break after the update.
Changelogs
For bugfix details, see the CHANGELOG.md in the codebase or these links:
Tooling
For general upgrade guidance, refer to the Hyvä Theme upgrade docs.