You don’t specify if you just want to watch on your computer or stream to an AppleTV or some other box. Other than what OS you’re running you’ve told us nothing about your set up. Are you streaming to a TV or watching on your computer? It makes a difference with more options on the streaming side than there may be for Mac OS. But…
If the files are DRM protected your options are limited to Apple’s software. There are third party apps out there (unsurprisingly they are not offered on the Mac App Store) that can strip the DRM from your files. It’s time consuming and morally questionable to do this however.
Why are you still on Mojave? An update, either OS or a newer Mac or both might help.