There is the possibilitty to choose custom bridge networks for any docker in the dropdown menue  of available networks.

It is required  to create a custom bridge network manually, you need to use CLI.

created a custom network with the name “my-bridge”.

docker network create my-bridge

or if you want a specific subnet for the bridge network

docker network create --subnet=192.168.255.0/24 my-bridge

if you want do delete a brige you need to disable all activ dockers that are using that bridge first.

docker network rm my-bridge

List off commands

connect – Connect a container to a network
create – Create a network
disconnect – Disconnect a container from a network
inspect  – Display detailed information on one or more networks
ls – List networks
prune – Remove all unused networks
rm – Remove one or more networks

Source:

https://forums.unraid.net/topic/70906-added-in-651-docker-user-defined-bridge-networks/