Marketing Cloud requires to have a link to the Profile Center. You can include it in your email by clicking on
then selecting Profile Center:

Otherwise, if you want to create one click unsubscribe button, you can use this AMPScript code:
%%[
VAR @sid, @jid, @listid, @batchid, @reason, @lue, @lue_prop, @lue_statusCode, @overallStatus, @requestId, @lue_Response, @lue_Status, @lue_Error
SET @emailaddr = AttributeValue("emailaddr")
SET @emailName = AttributeValue("emailname_")
SET @subKey = AttributeValue("_subscriberkey")
SET @jid = AttributeValue("jobid")
SET @batchid = AttributeValue("_JobSubscriberBatchID")
/* Set the listId here */
SET @listid = '21'
SET @reason = "PUT THE UNSUBSCRIBING REASON HERE"
SET @lue = CreateObject("ExecuteRequest")
SetObjectProperty(@lue,"Name","LogUnsubEvent")
SET @lue_prop = CreateObject("APIProperty")
SetObjectProperty(@lue_prop, "Name", "SubscriberKey")
SetObjectProperty(@lue_prop, "Value", @subKey)
AddObjectArrayItem(@lue, "Parameters", @lue_prop)
SET @lue_prop = CreateObject("APIProperty")
SetObjectProperty(@lue_prop, "Name", "JobID")
SetObjectProperty(@lue_prop, "Value", @jid)
AddObjectArrayItem(@lue, "Parameters", @lue_prop)
SET @lue_prop = CreateObject("APIProperty")
SetObjectProperty(@lue_prop, "Name", "ListID")
SetObjectProperty(@lue_prop, "Value", @listid)
AddObjectArrayItem(@lue, "Parameters", @lue_prop)
SET @lue_prop = CreateObject("APIProperty")
SetObjectProperty(@lue_prop, "Name", "BatchID")
SetObjectProperty(@lue_prop, "Value", @batchid)
AddObjectArrayItem(@lue, "Parameters", @lue_prop)
SET @lue_prop = CreateObject("APIProperty")
SetObjectProperty(@lue_prop, "Name", "Reason")
SetObjectProperty(@lue_prop, "Value", @reason)
AddObjectArrayItem(@lue, "Parameters", @lue_prop)
SET @lue_statusCode = InvokeExecute(@lue, @overallStatus, @requestId)
SET @lue_Response = Row(@lue_statusCode, 1)
SET @lue_Status = Field(@lue_Response,"StatusMessage")
SET @lue_Error = Field(@lue_Response,"ErrorCode")
]%%
Don't forget to update some details in the code as described in comments. You can find the AllSubscribers list id by going to Email Studio > Subscribers > AllSubscribers > Properties and grab the List ID.