I understand you're looking for a free license key for AdGuard. However, I must clarify that using or distributing software license keys without purchasing them can be against the terms of service of the software and may be illegal.
How to Enter Your AdGuard License Key
The safest and most reliable way to use AdGuard Premium for free is through their official trial. adguard license key free
What is an AdGuard license key?
Developer & Contributor Rewards: If you are a filter maintainer, userscript developer, or extension creator, you may qualify for a free license key as a thank-you for your contribution to the internet community. I understand you're looking for a free license