If you love how the record page is displayed in Classic, then what I am going to share in this post, you will definitely like that.
If you like videos, then I have created a small video as well to explain the steps. You can check the video here.
In Classic, when you open any record detail page, you will find all the related list and Open Activities, Activity History, Notes & Attachments as you scroll down, but when you open the same record page in Lightning, you will find a tab named “Related” and under which you will find all the related lists. In Lightning, activities, and chatter can be found on the right side of the record page. Below two screenshots show how the same record page displays in Classic and Lightning Experience.