How to add a custom button on the record detail page in salesforce

Problem: As an example, want to show a custom button on the account record detail page

Step 1: Create a custom button of type 'Detail Page Button' on the detail page object i.e. Account

Go to Setup --> Object Manager --> Account --> Buttons, Links and Actions section --> click on 'New Button or Link' as shown in the image below

Create a custom Button as shown below by making sure you select display type as 'Detail Page Button'.

Step 2: Go to the page layout of the detail page. In this example, associated account page layout.

Add the button to the 'Account Detail' section as shown in the image and save the layout.

Save the account page layout and then refresh the account record.

The custom button will now appear as shown in the image below