Trying to figure out some things about the Decoupled setup for CMS 11.20.7 on-premise.
Same code is deployed to all servers.
Licensing is per server and site, so you could have bought lincese for one site and additional server or servers (you need valid licenses also for customer test environments).
Also if you have decoupled setup, you usually want to run the scheduled jobs, only on the admin server. See documentation https://world.optimizely.com/documentation/developer-guides/archive/cms/configuration/Configuring-episerver/#applicationsettings and find the "enableScheduler" setting. So you would set that to false in web.config for the front-end server and on the admin config you would have it true, so the scheduled jobs are running only on the admin server and not the front-end (publically accessible server(s)).