I cannot login to my iMAC , I have my Apple ID , but the password isn’t the same to login into the desktop

Try the procedure in this Apple document: If you forgot your Mac login password

Something you might want to consider is after you set up your new computer and write down the really important stuff in a notebook you can lock up at home for a main Admin account. Then I recommend creating just a regular user account for all of the stuff you really don’t need Admin privileges for. I like having one just for web browsing, one for scanning documents that is always kept offline, others for this and that. The great thing about non admin accounts is you can keep the passwords a little more simple because they don’t have the privilege to run anything malicious if you get a bad email or website, they limit the amount of information available if compromised to just that account. Most of all you can sign in the Admin account and change any regular account passwords if you forget it. Just make sure you know where the admin password, the file vault key or any other hardware or system essential password you change or personalize and don’t use on a regular basis. Many would advise never to write that stuff down but it has saved me on really old computers after upgrading to a new computer. Just make sure you lock it up with passports, birth certificates and important stuff like that.