Texifier version 1.9.21 will be the last version supporting macOS Big Sur (macOS 11).
In the event that your app has automatically updated itself to a version of Texifier higher than 1.9.21, it may not launch. Please manually download version 1.9.21 from its release notes page and replace the app in your Applications folder with that version.
Note that if you update your macOS to a later version where Texifier is continued to be supported, the app will resume updates automatically.