Hello @Mohamed jihad bayali
Setting spending limit works on credit based subscriptions like free trial, visual studio offer type etc. where enabling the spending limit will recommend you to run your services on the same which will be within the monetary credits to avoid charges on pay-as-you-go.
There is no spending limit feature for Pay-As-You-Go and you will not be able to set it. Your understanding about budget is correct. That can be used to be vigilant about your Azure spending.
Hope this clarifies.
Kind regards
Divya.