The error message you're encountering indicates that the 'linux/susfs.h' header file is not found during the compilation of SukiSU Ultra. This file is essential for integrating SUSI-FS (SukiSU Filesystem) with the kernel. The error suggests that SUSI-FS has not been integrated into your kernel, which is a prerequisite for compiling SukiSU Ultra.

To resolve this issue, you should first ensure that SUSI-FS is properly integrated into your kernel. You can refer to the provided link [https://gitlab.com/simonpunk/susfs4ksu] for guidance on how to integrate SUSI-FS with your kernel. Once SUSI-FS is successfully integrated, the 'linux/susfs.h' header file should be available, and the compilation process for SukiSU Ultra should proceed without this error.

Additionally, make sure that you have the correct version of SUSI-FS that is compatible with your kernel version and type. If you're using a Non-GKI kernel, ensure that you have the appropriate version of SUSI-FS that supports Non-GKI. If you continue to face issues, you may need to consult the documentation or seek support from the SukiSU community for further assistance.