The currently releases version of this utility immediately aborts on execution. 

This appears to be caused by certain calls to sysconf do not return expected values.

Its been fixed upstream in the release, but won't be available until a version after 1.94. 

The patch below can be applied to the port to correct this:

root@freebsd:/usr/ports/sysutils/fusefs-s3fs # cat files/patch-src_s3fs__util.cpp 
--- src/s3fs_util.cpp.orig      2024-08-25 21:19:25 UTC
+++ src/s3fs_util.cpp
@@ -65,6 +65,7 @@ void init_sysconf_vars()
     // there is no hard limit on the size of the buffer needed to
     // store all the groups returned.
 
+    errno = 0;
     long res = sysconf(_SC_GETPW_R_SIZE_MAX);
     if(0 > res){
         if (errno != 0){
@@ -75,6 +76,7 @@ void init_sysconf_vars()
     }
     max_password_size = res;
 
+    errno = 0;
     res = sysconf(_SC_GETGR_R_SIZE_MAX);
     if(0 > res) {
         if (errno != 0) {

Please let me know next steps. I'll be happy to update the port if needed.