How do you remove certain selections of shipping carrier from the admin shipping section?
We are based in the UK. We added Royal Mail and DPD via a module. We don't want United States Postal Service or DHL to show here.
To remove shipping career from the backend. you need to disable the modules from the Magento core modules. For that you can use commands PHP bin/magento module:disable (module name) Or you can disable from the core config file.
But it is not advisable as you disable such module which is available in core Magento may you face some issues.
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You can Disable the SHipping Method
To disable any shipping method like flat rate: Goto Admin > Store > Configuration > Click on Shipping methods under Sales tab, it will show you all methods. Here you can disabled any method by setting "Enabled" option to No and click save config button.