I'm playing on 1.21.5 on fabric (unsure which version of fabric) and I have the fence gates option turned on and it just will not work. If you could manage to fix this in 1.21.6's verison that'll be great.

Thanks for opening the issue! This has been fixed in version 7.0 of Double Doors, alongside some other features. Appreciate it.

https://curseforge.com/minecraft/mc-mods/double-doors/files