I have a side quest account and it sends me to this page to download deisim. I read the description and it only has download files for windows and android. Is this app available for Mac?

If you want to install the game on your quest you need to take the android .apk file and install it with adb or SideQuest for more convenience.
There is a mac version of sidequest available here : https://sidequestvr.com/setup-howto