@TitusPiJean I'm not sure if you are maintaining this LDAP extension, but I've made a PR to fix multiple issues and overhaul the settings to allow multiple LDAP domains.
Images of the fixes is here:
tituspijean/flarum-ext-auth-ldap109
Currently there is a bug on select2 multiple selectbox for the searchFields and nicknameFields, hopefully it be fixed soon. Fixed
This has been tested and working on Flarum 1.8.5, tested with two different LDAP domains.