Quickly skimming the readme, it states:

• OAuth token spoofing: To circumvent rate limits imposed by Reddit, OAuth token spoofing is used to mimick the most common iOS and Android clients. While spoofing both iOS and Android clients was explored, only the Android client was chosen due to content restrictions when using an anonymous iOS client.
• Token refreshing: The authentication token is refreshed every 24 hours, emulating the behavior of the official Android app.
• HTTP header mimicking: Efforts are made to send along as many of the official app’s headers as possible to reduce the likelihood of Reddit’s crackdown on Redlib’s requests.

Quad9 doesn’t report it as being blocked. https://quad9.net/result?url=catbox.moe

You can block instances. Go to settings, blocks, in block instance section search for the instance that you want to block.