How to check is CSS merge enabled programmatically Magento 2?

Check CSS Merge is enabled or not using Magento 2 by isMergeCssFiles() method.

To Merge CSS files in Magento 2 via admin panel,
Go To Admin panel,
Click Stores -> Settings -> Configuration from the left sidebar.
Click on Advanced -> Select Developer Tab,
Open the CSS Settings section,
Choose Yes from the Merge CSS Files.
Click on Save Config from the top right.

You can Check whether merging of CSS files is on using programmatically,

echo $this->isCssMergeEnabled(); // result bool

You got the result as true or false using the above line for CSS Merge.
Output:
Boolean