In openSUSE Leap 15.4 / SLE 15 SP4 BETA,
I have found what appears to be a bug in the source code of the F2FS in default
Kernel (5.14.21-150400.22).

When using the default Linux kernel source code,
a bug in the source code causes a compile error when building the F2FS kernel
module.

First, install kernel-source.
   sudo zypper install kernel-source

Next, modify the /usr/src/linux-5.14.21-150400.22/fs/f2fs/file.c as follows.
   (Lines 1093 and 1101)  
   * before  
   filemap_invalidate_lock(mapping)  

   * after
   filemap_invalidate_lock(inode->i_mapping)

The F2FS kernel module can now be built.