Your Ae comp is probably too small

Regardless of what your Figma frame is designed at, be sure your Ae comp is set to the intended output size, then enable Scale art to comp width by right-clicking in the Overlord Ae extension. This will scale up all your art proportionally to the width difference between Ae and Figma frames.

Vector art scales infinitely, right?

It's pretty common for UI designers to work at a base pixel value and allow the device's pixel density to handle the up-scaling of art. And since Figma is a resolution independent design app, that is perfectly ok.

Yes, After Effects supports vectors in the form of shape layers, text, and imported Illustrator files and SVGs. BUTTTT Ae is first and foremost a raster art application. So that means you can scale up vector art infinitely within a comp, but once you go above 100% of your composition's zoom it's gonna be pixelated.

How do I fix it?

The workaround is to manually adjust the comp size (⌘/CTRL+K) and let Overlord scale up the art correctly with the setting above.

If you used the New Comp button then the new comp will be exactly the pixel size as your design. You can then add the pixel density values by locking the aspect ratio and typing *2 or *3 for 2x and 3x pixel densities.

390:844 * 3 = 1170:2532

Then when you enable Scale art to comp width in the Overlord preferences, the art will scale up to match the Ae comp width and not be blurry.