Yes, if you have implemented google tag manager on your site there is no need of google analytics id. Because Google Tag Manager is capable of doing more things for you and it can track everything a user does on your site. once the GTM container is inserted on your site you can connect google analytics using tag manager to view reports. Learn how to connect google analytics using google tag manager.
Regardless of niche, the customer engagement analytics process is always the same. People are coming to your website