FreeBSD has a /dev/cuse device, and a libcuse reimplemented on top of it, but it uses a different protocol from Linux's CUSE. You can see the FreeBSD implementation at https://github.com/freebsd/freebsd-src/blob/release/13.1.0/s... -- note how cuse_server_read() and cuse_server_write() are stubs.
I am somewhat familiar with this because I wrote a FUSE/CUSE server library in Rust, and tried porting it to FreeBSD. The FUSE bits worked with only minor issues[0][1], but the CUSE bits were completely different so I had to turn off that part of the library for FreeBSD targets.