It sounds like you're experiencing some compatibility issues with your Poco F5 device running Derpfest ROM with the 912 kernel. The problem arises when you try to flash Pixelify or Integrity Fix, which are dependent on Zygisk. After the flashing and rebooting process, you're unable to access the Zygisk next web UI and also face issues with Google search. This situation persists until you uninstall Zygisk. You've already tried uninstalling AdGuard and all CA certificates, but the problem remains unresolved. It seems like there might be a deeper conflict between the ROM, the kernel, and the Zygisk modules. To troubleshoot this further, consider the following steps:

  1. Check for Updates: Ensure that your Derpfest ROM and all the modules (Pixelify, Integrity Fix, etc.) are up to date. Sometimes, compatibility issues are resolved in newer versions.
  2. Kernel Compatibility: Verify if the 912 kernel is fully compatible with the Zygisk modules you're using. Sometimes, certain kernels might have issues with specific mods.
  3. Log Files: Look into the log files for any error messages that could provide more insight into what's going wrong. Tools like logcat can help you view these logs.
  4. Community Forums: Check out forums related to Derpfest ROM or Poco F5. Other users might have encountered and resolved similar issues.
  5. Reinstallation: As a last resort, you might consider a clean reinstall of your ROM and Zygisk. Make sure to back up your data before doing so.

By following these steps, you should be able to identify and resolve the issue. If the problem still persists, it might be worth reaching out to the developers of Derpfest ROM or the Zygisk community for further assistance.