Setting text at 20% opacity looks like a watermark, not UI text. If you have to squint to read it, you have gone too far. The user should be able to read the paralucent text effortlessly at a glance; they just shouldn't be drawn to it.
The exact opacity depends on your background. Use this guide: paralucent text
If you meant something else by “paralucent” (like a specific app, font, or brand term), let me know and I’ll refine this. Setting text at 20% opacity looks like a
The Paralucent Text family differs from the standard and display weights through several key technical adjustments intended for long-form reading and small-scale applications: or brand term)