Short answer: Uploading fonts needs Canva Pro (or Teams): go to Brand, open your Brand Kit, and upload the .ttf under Fonts. On a free account, download your text as a PNG here and upload it as an image.
With Canva Pro or Teams
- Download the font from the generator and extract the ZIP.
- In Canva, open Brand and choose your Brand Kit.
- Under Fonts, choose Upload a font and pick the .ttf. Canva asks you to confirm you're allowed to use it: these fonts are open-source, so you are.
- The font now appears at the top of the font list in every design.
On a free Canva account
Free accounts can't upload fonts, but they can upload images. Download your styled text as a PNG from the generator, then in Canva go to Uploads, upload the PNG, and drag it onto your thumbnail. It has a transparent background, so only the text shows.
The PNG is high resolution, so you can scale it up to fill a 1280 × 720 thumbnail without it going blurry.