I'm just going to go ahead and say it. The fonts available in Cricut Design Space are somewhat limited. I assumed this was a problem without a solution, until I realized there is a whole world of downloadable fonts on the internet. And guess what, y'all? They're all able to be used in your Cricut projects! WHOA.
I typically start by googling what type of font I'm looking for, "calligraphy fonts" for example, and search until I find a downloadable file that I like. A site called dafont.com is also a great resource; they have almost 60,000 downloadable fonts that are free for personal use.
Once you find a font that tickles your fancy, download and then open the zip folder. Find the file listed under file type "True Type Font File" and double-click to open it. In the top lefthand corner of the window that opens, click Install. These instructions are geared towards Windows, but a quick google search can probably translate for all y'all Apple users!
The next time you're in Cricut Design Space, your new font will automatically show up under system fonts! As a heads up, if you downloaded the font while having Design Space open, you'll likely need to close out of the application and reopen it.
Custom fonts can really take your Cricut projects to a whole 'notha level, so take a look around some font sites and get inspired!