In order to mount locally a remote archive or an entire repository as a FUSE
filesystem, it is required to load fuse module:

# kldload fuse

To load the module at boot time, add

fuse_load="YES"

to /boot/loader.conf by running:

sysrc fuse_load="YES"

Also, if you plan to mount borg repositories as non root user, you need to run

# sysctl vfs.usermount=1

and add the line

vfs.usermount=1

to /etc/sysctl.conf to ensure the setting is loaded at boot time.