Update The Subscriber in Sales cloud When UnSubscribed In Marketing Cloud

As stated /linked, CloudPagesURL() can be used for encrypting parameters sent from an email, and requestParameter can auto-decrypt parameters encryted through CloudPagesURL().

On your form page, send a post request to a handler page. There, again you can use requestParameter().

more on form / handler: Issue with passing value to data extension from the marketing cloud page

Then, on your handler page you need a LogUnsubEvent call. That will auto-populate "hasoptedOutOfEmail" to true. see also:

https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-programmatic-content.meta/mc-programmatic-content/unsubEvent.htm

Sales Cloud to Marketing Cloud unsubscribe synching

Firstly, you will need a handler page to write your ampscript to update the relevant fields in Salesforce. Because ampscript works on the load of the cloud page.This handler page will load once the user clicks on Submit. This will contain all the required ampscript and optionally a thankyou/confirmation message to the user. To answer your question, on how to pass the recordid, you need to pass it as a paramter to the handler page and then use RequestParameter to fetch it. Also, you will need additional parameters like email address, subscriber key to be passed in order to unsubscribe withing Marketing Cloud. As a security concern, encode/encrypt these parameters. You can find some sample codes here.