There are many ways to get different shapes in Blender. One of the easiest ways to get circle holes is to use LoopTools add-on. Lets see how it looks using Boolean, too.

Be sure to go under Edit, Preferences, Add-ons, and search for Mesh: LoopTools. Enable it and save your settings.

Selecting vertices now you can right-click and go under LoopTools to change your shape. It's the best way to keep your geometry! And get quads!

Follow for more quick tips.